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Datasheet

Theba pisana
(white garden snail)

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Datasheet

Theba pisana (white garden snail)

Summary

  • Last modified
  • 03 December 2019
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Theba pisana
  • Preferred Common Name
  • white garden snail
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Mollusca
  •       Class: Gastropoda
  •         Subclass: Pulmonata
  • Summary of Invasiveness
  • T. pisana is a medium-sized snail with a sub-globular, generally white or off-white shell that often bears a complex pattern of darker markings. It is generally a species of coastal habitats with warm to hot an...

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Pictures

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PictureTitleCaptionCopyright
Theba pisana (white garden snail); two adult shells, showing polymorphism.
TitleAdult shells
CaptionTheba pisana (white garden snail); two adult shells, showing polymorphism.
Copyright©Robert H. Cowie
Theba pisana (white garden snail); two adult shells, showing polymorphism.
Adult shellsTheba pisana (white garden snail); two adult shells, showing polymorphism.©Robert H. Cowie
Theba pisana (white garden snail); an aggregation of snails on vegetation. Tenby, Wales, UK.
TitleAggregation
CaptionTheba pisana (white garden snail); an aggregation of snails on vegetation. Tenby, Wales, UK.
Copyright©Robert H. Cowie
Theba pisana (white garden snail); an aggregation of snails on vegetation. Tenby, Wales, UK.
AggregationTheba pisana (white garden snail); an aggregation of snails on vegetation. Tenby, Wales, UK.©Robert H. Cowie
Theba pisana (white garden snail); close-up of an aggregation of snails on vegetation. Tenby, Wales, UK.
TitleAggregation
CaptionTheba pisana (white garden snail); close-up of an aggregation of snails on vegetation. Tenby, Wales, UK.
Copyright©Robert H. Cowie
Theba pisana (white garden snail); close-up of an aggregation of snails on vegetation. Tenby, Wales, UK.
AggregationTheba pisana (white garden snail); close-up of an aggregation of snails on vegetation. Tenby, Wales, UK.©Robert H. Cowie
Theba pisana (white garden snail); aggregation aestivating on pine sapling. Rethymno (Rethymnon), Crete. August, 2011.
TitleAestivating aggregation
CaptionTheba pisana (white garden snail); aggregation aestivating on pine sapling. Rethymno (Rethymnon), Crete. August, 2011.
Copyright©A.R. Pittaway
Theba pisana (white garden snail); aggregation aestivating on pine sapling. Rethymno (Rethymnon), Crete. August, 2011.
Aestivating aggregationTheba pisana (white garden snail); aggregation aestivating on pine sapling. Rethymno (Rethymnon), Crete. August, 2011.©A.R. Pittaway
Theba pisana (white garden snail); large aggregation aestivating in doorway. Rethymno (Rethymnon), Crete. August, 2011.
TitleAestivating aggregation
CaptionTheba pisana (white garden snail); large aggregation aestivating in doorway. Rethymno (Rethymnon), Crete. August, 2011.
Copyright©A.R. Pittaway
Theba pisana (white garden snail); large aggregation aestivating in doorway. Rethymno (Rethymnon), Crete. August, 2011.
Aestivating aggregationTheba pisana (white garden snail); large aggregation aestivating in doorway. Rethymno (Rethymnon), Crete. August, 2011.©A.R. Pittaway
Theba pisana (white garden snail); large aggregation, aestivating on plants. Rethymno (Rethymnon), Crete. August, 2011.
TitleAestivating aggregation
CaptionTheba pisana (white garden snail); large aggregation, aestivating on plants. Rethymno (Rethymnon), Crete. August, 2011.
Copyright©A.R. Pittaway
Theba pisana (white garden snail); large aggregation, aestivating on plants. Rethymno (Rethymnon), Crete. August, 2011.
Aestivating aggregationTheba pisana (white garden snail); large aggregation, aestivating on plants. Rethymno (Rethymnon), Crete. August, 2011.©A.R. Pittaway

Identity

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Preferred Scientific Name

  • Theba pisana (O. F. Muller, 1774)

Preferred Common Name

  • white garden snail

Other Scientific Names

  • Euparypha pisana (O.F.MUELLER)
  • Helix (Euparypha) pisana O. F. Muller, 1774
  • Helix pisana O. F. Muller, 1774

International Common Names

  • English: citrus tree snail; grey snail; Italian white snail; Mediterranean coastal snail; Mediterranean snail; Mediterranean white snail; sand hill snail; snail, Mediterranean white; snail, sandhill; snail, white garden; white sand hill snail; white snail
  • Spanish: caracol avellanench; caracol blanco; caracol mediterraneo; caracolillo blanco de la arena
  • French: cagouille en charente; escargot blanc; escargot blanc, petit; morguette en provence

Local Common Names

  • Germany: Schnecke, Mittelmeersand-
  • Israel: chilzonit hagina
  • Italy: babbaluciu; babbuccia latina; chiocciola delle dune; cozze nude; vavaluciu duci
  • South Africa: duineslak

EPPO code

  • THEBPI (Theba pisana)

Summary of Invasiveness

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T. pisana is a medium-sized snail with a sub-globular, generally white or off-white shell that often bears a complex pattern of darker markings. It is generally a species of coastal habitats with warm to hot and arid climates, although it extends into cooler and wetter habitats in northwest Europe. Its range includes almost all the Mediterranean coastline, extending up the Atlantic coast of Europe. The extent to which this range is natural is not certain. Morocco has been suggested as its region of origin. Beyond this European/Mediterranean range, the major regions to which it has been introduced are South Africa (first recorded 1881), Australia (1890s) and California (1914), in all three regions rapidly becoming an invasive pest. It is frequently intercepted by quarantine officials both associated with shipments of goods and in personal luggage, indicating that it is both accidentally and deliberately transported over long distances. It is also readily transported relatively short distances, for instance attached to vehicles. Once introduced, its high rate of growth and reproduction and ability to reach extremely high population densities make it a potentially serious and difficult to control pest. It is listed as a potential pest of quarantine significance in the United States.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Mollusca
  •             Class: Gastropoda
  •                 Subclass: Pulmonata
  •                     Order: Stylommatophora
  •                         Suborder: Sigmurethra
  •                             Unknown: Helicoidea
  •                                 Family: Helicidae
  •                                     Genus: Theba
  •                                         Species: Theba pisana

Notes on Taxonomy and Nomenclature

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The white garden snail was first described scientifically as Helix pisana by Müller (1774). The genus Theba was introduced by Risso (1826) and H. pisana was placed within it. Hartmann (1844 [in 1840-1844]) placed it in his new monotypic subgenus Euparypha (of Helix) as a synonym of Helix rhodostoma Draparnaud, 1801. It was then generally retained in Euparypha (e.g. Gude and Woodward, 1921). However, the International Commission on Zoological Nomenclature (ICZN, 1956) determined that Euparypha Hartmann, 1844 was a junior objective synonym of Theba Risso, 1826; Theba was placed on the ‘Official List of Specific Names in Zoology’, with Theba pisana as the type species, and Euparypha was placed on the ‘Official Index of Rejected and Invalid Generic Names in Zoology’. The correct name is therefore Theba pisana. This ICZN determination took some time to be recognized by those working with the species, many of whom continued to call it Euparypha pisana. However, it is now almost always referred to correctly as Theba pisana.

From time to time it has been placed in various other genera, viz. Heliomanes, Carocolla, Xerophila, Cochlea, Tropidocochlis and Teba, the last being an incorrect subsequent spelling of Theba (Cowie, 1982; Bouchet and Rocroi, 2004).
 
T. pisana is very variable in terms of its shell appearance, primarily in the patterning of bands and other markings on the shell. By the start of the twentieth century, no fewer than 27 ‘species’, all in fact referable to pisana, had been described (Germain, 1908; Taylor, 1906-1914). Extensive synonymies have been given by Germain (1908, 1929, 1930) and Kennard and Woodward (1926), as well as by Taylor (1906-1914), who also dealt with the plethora of varietal and sub-varietal names given to shells with subtle differences in shell shape and colour/pattern, few of which have any taxonomic meaning, as Taylor recognized, but are purely descriptive of the immense range of variation especially in shell colour/pattern.

The most recent comprehensive taxonomic treatment of the genus Theba is by Gittenberger and Ripken (1987). Four fossil and ten Recent species are recognized. Because of variation within some of the species there are 17 species and subspecies in total. How many of the subspecies are valid is open to debate. All species and subspecies, with the exception of T. pisana pisana are restricted to small geographical areas in Morocco, the western Sahara, the southernmost part of the Iberian peninsula and the Canary and Salvage Islands (Bachuys, 1972; Gittenberger and Ripken, 1987).

Description

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The following is taken in part and modified from Kerney and Cameron (1979), Cain (1984) and Cowie (1984a). More detail is provided by Taylor (1906-1914). Adult shell up to 20 mm high and 25 mm wide, though rarely this big and more normally around 15-18 mm wide. Shell slightly depressed globular (wider than high), with 5½-6 slightly convex whorls with shallow sutures. Umbilicus narrow, and partly obscured by reflected columellar lip. Mouth of adult shell elliptical, with an internal thickening (no outwardly reflected lip) and sometimes a pinkish flush. Juvenile shell with a sharp keel at the periphery (mid-line of the shell), becoming rounded as the shell grows to adulthood. Shell sculpture of growth-ridges crossed by fine spiral striations. Shell white or off-white, rarely pink, either plain or with spiral patterning of lines (translucent, pale yellowish, dark brown or blackish), which may be broken transversely into dots and dashes, augmented with feathering along their edges, or fused to varying extents producing arrow-head shapes, chevrons and blocks. Patterning may only appear on later whorls.

Distribution

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T. pisana is generally a species of coastal, often sandy (e.g. dunes) habitats with warm to hot and arid climates. Its range includes almost all the Mediterranean coastline, extending up the Atlantic coast of Europe as far as the southernmost part of the Netherlands, southwest England and Wales and eastern Ireland, and to the Madeiran (records on the Salvages are in fact of a different Theba species; Gittenberger and Ripken, 1987) and Canary archipelagos, especially in sandy areas close to the sea. It extends inland notably in Spain, Portugal, southern and western France, Italy, Algeria and Morocco, although it is generally less abundant in such localities than it is near the coasts (Taylor, 1906-1914; Cowie, 1990).
 
Although reported in Germany (Godan, 1983), whether it ever became established is doubtful (R Cowie, University of Hawaii, USA, personal communication, 2009). It is almost certainly present in Monaco due to presence all along this part of the French and Italian coasts (R Cowie, University of Hawaii, USA, personal communication, 2009).

It has been suggested on various bases, including the occurrence of other Theba species only in northwest Africa, that the original natural range of T. pisana was confined to Morocco (Sacchi, 1971; Welter-Schultes, 1998). However, it is possible that most of its current North African, Mediterranean and western European range is natural (Dürr, 1946; Baker and Vogelzang, 1988; Roth and Sadeghian, 2003), although possibly a result of post-glacial expansion from Morocco (Sacchi, 1971). Alternatively, at least some, if not most of its circum Mediterranean and western European distribution is a result of human activities in historic times and therefore T. pisana should be considered invasive in these areas where it may reach extremely high abundances. For the most part, the issue is unresolved (Gittenberger and Ripken, 1987), although there is some evidence and conjecture regarding specific regions (see History of Introduction/Spread).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 23 Apr 2020
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

AlgeriaPresentEPPO (2020); Sacchi (1971); Cowie (1982); Baker (1986); CABI (Undated)
BotswanaPresentEPPO (2020)
Cabo VerdeAbsent, Unconfirmed presence record(s)Baker (1986)
EgyptPresentEPPO (2020); Cowie (1990); CABI (Undated)
EthiopiaPresentEPPO (2020)
LibyaPresentEPPO (2020); Sacchi (1971); Godan (1983)
MauritaniaAbsent, Invalid presence record(s)Cowie (1982); Cowie (1984a)Gittenberger and Ripken (1987) only recorded T. pisana as far south as southern Morocco, and not even in Western Sahara
MoroccoPresentGittenberger and Ripken (1987); Cowie (1990); EPPO (2020)
MozambiquePresentEPPO (2020); Joubert and Walters (1951); Bruggen (1964)
NamibiaPresentEPPO (2020); Sanderson and Sirgel (2002)
SomaliaPresentEPPO (2020); Spence (1938); CABI (Undated)
South AfricaPresentEPPO (2020); Dürr (1946); Joubert and Walters (1951); Quick (1952); McQuaid et al. (1979); Sanderson and Sirgel (2002); CABI (Undated)
SudanPresentEPPO (2020)
TunisiaPresentEPPO (2020); Germain (1908); Sacchi (1971)
ZimbabwePresentEPPO (2020)

Asia

GeorgiaAbsent, Unconfirmed presence record(s)CABI (Undated)Unreliable because this is so far inland and so far from the rest of its Eurasian distribution; Original citation: Taylor (1906-1914)
IraqPresentEPPO (2020)
IsraelPresentEPPO (2020); Heller and Tchernov (1978); Cowie (1982); Cowie (1983); Cowie (1984); Baker (1986); Johnson (1988); Cowie (1990); CABI (Undated)
JordanPresentEPPO (2020)
LebanonPresentEPPO (2020); Sacchi (1971); CABI (Undated)
Saudi ArabiaPresentEPPO (2020); Godan (1983)
SyriaPresentEPPO (2020); Germain (1908)
TurkeyPresentEPPO (2020); Cowie (1990); CABI (Undated)
YemenPresentEPPO (2020)

Europe

AlbaniaPresentEPPO (2020); Dhora and Welter-Schultes (1996); Bank (2007)
BelgiumPresent, LocalizedDeblock (1962); Deblock and Hoestlandt (1967); Bank (2007); CABI (Undated)
Bosnia and HerzegovinaPresentSacchi (1971)Based only on a sketch map of distribution
CroatiaPresentSacchi (1971); CABI (Undated)
CyprusPresent, LocalizedCowie (1982); Cowie (1983); Cowie (1990); CABI (Undated)
DenmarkAbsentEPPO (2020)
FrancePresentEPPO (2020); Germain (1930); Deblock (1962); Cowie (1982); Cowie (1983); Cain (1984); Johnson (1988); Cowie (1990); Bank (2007); CABI (Undated)
-CorsicaPresentGermain (1930); Bank (2007)
GermanyPresentGodan (1983); CABI (Undated)
GibraltarPresentGittenberger and Ripken (1987); Bank (2007); CABI (Undated)
GreecePresentEPPO (2020); Cowie (1982); Cowie (1983); Cowie (1984); Cowie (1990); Welter-Schultes (1998); Bank (2007); CABI (Undated)
IrelandPresentEPPO (2020); Deblock (1962); Bank (2007); CABI (Undated)
ItalyPresentEPPO (2020); Sacchi (1971); Cowie (1982); Cowie (1983); Cowie (1984); Baker (1986); Cowie (1990); Bank (2007); CABI (Undated)
-SicilyPresentEPPO (2020)
MaltaPresentHunt (1997); Bank (2007); CABI (Undated)
MonacoAbsent, Unconfirmed presence record(s)Godan (1983)Intercepted by Canadian authorities on plants and plant products originating in Monaco
MontenegroPresentSacchi (1971); Bank (2007)
NetherlandsPresentEPPO (2020); Gittenberger and Ripken (1987); Bank (2007)
North MacedoniaPresentBank (2007)
PortugalPresent, WidespreadCABI (Undated); Cowie (1990); Bank (2007)Many localities; Original citation: Taylor (1906-1914)
-AzoresPresentBank (2007); Cameron et al. (2007); CABI (Undated)
-MadeiraPresentGermain (1908); Gittenberger and Ripken (1987); Cowie (1990); Cameron and Cook (2001); Cameron et al. (2006); Bank (2007); Cameron et al. (2007); CABI (Undated)
SerbiaPresentEPPO (2020)
SloveniaPresentSacchi (1971); CABI (Undated)
SpainPresentEPPO (2020); Cowie (1982); Cain (1984); Cowie (1984); Gittenberger and Ripken (1987); Cowie (1990); Bank (2007); CABI (Undated)
-Balearic IslandsPresent, LocalizedCowie (1982); Cowie (1983); Cain (1984); Cowie (1990); Bank (2007); CABI (Undated)
-Canary IslandsPresentGermain (1908); Gittenberger and Ripken (1987); Cowie (1990); Bank (2007); CABI (Undated)
SwitzerlandPresentEPPO (2020); Baker (1986); CABI (Undated)
United KingdomPresent, LocalizedEPPO (2020); Pennant (1777); Deblock (1962); Cowie (1982); Humphreys et al. (1982); Cowie (1983); Cowie (1984); Cowie (1986); Cowie (1987); Fowles and Cowie (1989); Cowie (1990); CABI (Undated)
-Channel IslandsPresent, LocalizedBarrett (1972); Barrett (1975); Cowie (1982); Bank (2007); CABI (Undated)
-EnglandPresent, LocalizedEPPO (2020)

North America

BermudaAbsent, Formerly presentPeile (1926); Godan (1983)
United StatesPresent, LocalizedEPPO (2020)
-CaliforniaPresent, LocalizedEPPO (2020); Chace (1915); Basinger (1927); Gammon (1943); Armitage (1949); Mead (1971); Cowie (1987); Cowie (1990); Roth and Sadeghian (2003)

Oceania

AustraliaPresent, LocalizedEPPO (2020)
-New South WalesPresentIntroducedBaker (1986); Baker (2002)
-South AustraliaPresent, WidespreadIntroduced1928InvasiveBaker (1986); Baker (2002)Southeast near the mouth of the River Murray, on Yorke Peninsula and Eyre Peninsula
-TasmaniaPresentBaker (1986); Johnson (1988)
-VictoriaPresentQuick (1953); Baker (1986); Johnson (1988); Baker (2002)
-Western AustraliaPresent, WidespreadIntroducedInvasiveBaker (1986); Quick (1953); Johnson (1988); Cowie (1990)Coastal areas of the southwest ranging from Northampton in the north to around Eucla in the east

South America

BrazilAbsent, Formerly presentEPPO (2020)

History of Introduction and Spread

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The spread of T. pisana around the Mediterranean and northwards up the coast of western Europe from its presumed origin in Morocco was probably for the most part post-glacial with some more recent introductions the result of human activities, notably in the northernmost parts of the range. However, little is known of the chronology of introduction or spread, or of the geographic sources. Much of the following information is highly conjectural.
 
In the Mediterranean, T. pisana has been reported from Pliocene deposits in Algeria (Taylor, 1906-1914) but the true identity of this material is uncertain so this may not represent part of its original natural distribution (Gittenberger and Ripken, 1987). It has not been found in Pleistocene deposits in Israel so it is probably a “historic” introduction there (Heller and Tchernov, 1978). Welter-Schultes and Williams (1999) explicitly considered T. pisana as non-native in their studies in the Greek Islands, but with no explanation. It has been found in deposits in Malta dating to as early as the second or third centuries AD but not earlier (Hunt, 1997) so may be a Roman introduction. In the Channel Islands, France, Italy (Sicily), the Balearic Islands (Majorca), Madeira and the Canary Islands (Fuerteventura) it has been reported in Holocene deposits of unspecified age (Taylor, 1906-1914) but whether truly fossil or the result of mixing of strata involving modern shells is not known, as was hinted at by Taylor (1906-1914) regarding Madeira.
 
Its entire northwest European distribution may be fairly recent, although this has been demonstrated or inferred on a sound basis for only a few locations. It was deliberately introduced to the English Channel coast of Belgium (Ostend) in 1868 from Algeria (Taylor, 1906-1914) and this was mentioned by Deblock (1962) and Deblock and Hoestlandt (1967) as the possible source of the northern French and Belgian populations. It was not then reported from Belgium until 1934 (Deblock, 1962). These Belgian populations were considered by Deblock (1962) to be the northernmost populations, so the introduction of T. pisana to the Netherlands, considered to have occurred “quite recently” by Gittenberger and Ripken (1987), probably took place between 1962 and 1987. Taylor (1906-1914) and Deblock (1962) mentioned that T. pisana had been found in Pleistocene dunes in northern France near the Belgian border close to the English Channel, but this report and accurate dating of the shells has not been verified. Introduction to the Channel island of Guernsey was from Jersey in 1860, deliberately for “naturalization” (Taylor, 1906-1914; Barrett, 1972). If its presence in Jersey is as a result of an introduction, then this occurred before 1912, as it was recorded there by Taylor (1912 in 1906-1914), who also reported it in pre-Neolithic deposits. The origins of the UK populations are probably post-glacial (Cowie, 1982), although whether T. pisana arrived naturally or by human-assisted means is not clear. There have been suggestions that it may have been introduced to the UK during or prior to the eighteenth century in association with dry ballast discharged from ships, in association with the pottery trade between England and continental Europe, or as food brought by travellers, traders or sailors (Kerney, 1966; Turk, 1966, 1972; Cowie, 1982). Stelfox and McMillan (1966) suggested this last mechanism for the introduction of the species to Ireland.
 
The introduced or native status of other populations in North Africa, around the Mediterranean and in western Europe is unknown and, other than as summarized above, the detailed chronology, mechanisms and sources of introduction and spread in this Mediterranean/European region are almost entirely unknown.
 
The following comments relate to the distribution further afield to areas in which T. pisana is known definitively to have been introduced as a result of human activities. In almost no case is the reason for introduction (deliberate or accidental) known.

T. pisana was first recorded in South Africa in 1881 (McQuaid et al., 1979) and rapidly became abundant and widespread (Swanton, 1902; Conolly, 1916; Spence, 1938). It was introduced to Australia (Western Australia) probably in the 1890s (Johnson, 1988). By 1928 it was recorded in South Australia (Baker, 1986), subsequently reaching Victoria, New South Wales and Tasmania (Quick, 1953; Baker, 1986). It was first recorded in California in 1914 in San Diego County, considered invasive by 1923, and subsequently spread, in part with hay used as mulch in citrus groves (Hanna, 1966), to Orange and Los Angeles counties (Basinger, 1923, 1927; Gammon, 1943). It was purportedly eradicated (Armitage, 1949) but has since re-appeared, first in 1966 (Mead, 1971), although this re-appearance was hardly reported, and again in 1985 (Cowie, 1987). It now seems to be established, though only in San Diego County (Cowie, 1987; Roth et al., 1987; Roth and Sadeghian, 2003).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Belgium Algeria 1868 No No Taylor (1906); Taylor (1906-1914) Deliberate introduction
Belgium Algeria around 1867 No No Deblock (1962) Deliberate introduction to observe their capacity for adaptation, led to their distribution between Ostend and Westende
Belgium France pre-1934 No No Deblock (1962) Probably accidental (perhaps natural) - an extension of the northern French range
Bermuda pre-1926 No No Peile (1926) Not known whether deliberate or accidental, but probably accidental
California pre-1914 Food (pathway cause) ,
Ornamental purposes (pathway cause)
Yes No Armitage (1949); Basinger (1927); Chace (1915); Gammon (1943); Mead (1961) Probably deliberate, and probably from the Meditteranean / western Europe with Sicily specifically mentioned (1st introduction)
California 1949-1966 No No Mead (1971) Not known whether deliberate or accidental, but probably accidental. Possibly a remnant of the first introduction
California < or =1985 Yes No Cowie (1987) Not known whether deliberate of accidental, but probably accidental. Possibly a remnant of the first introduction
Germany Morocco post 1945 No No Godan (1983) Introduced accidentally associated with cargo or luggage
Germany Spain post 1945 No No Godan (1983) Introduced accidentally associated with cargo or luggage
Ireland pre-1818 Yes No Cowie (1982); Stelfox and McMillan (1966); Taylor (1906); Taylor (1906-1914) Perhaps introduced accidentally having been carried there as food by travellers, traders or fishermen from continental Europe
Malta   Yes No Hunt (1997) Not known whether deliberate or accidental (2nd or 3rd century)
Netherlands 1962-1987 Yes No Gittenberger and Ripken (1987) Probably accidental. Dates inferred since Belgium was considered the northermost limit by Deblock (1962)
Somalia before 1912 No No Taylor (1906); Taylor (1906-1914) The reference to Somalia was published in 1912
South Africa Europe 1881 Yes No Dürr (1946); Joubert and Walters (1951); McQuaid et al. (1979) Not known whether deliberate or accidental, but probably accidental
South Australia 1928 Yes No Baker (1986) Not known whether deliberate or accidental, but probably accidental
UK   Yes No Cowie (1982); Evans (1972); Kerney (1966); Turk (1966); Turk (1972) Not known whether introduced or arrived naturally, but probably the former. Though whether deliberately or accidentally is not known, Post-glacial or may have arrived only a few centuries ago
Victoria pre-1953 No No Quick (1953) Not known whether deliberate or accidental, but probably accidental
Western Australia 1890s Yes No Johnson (1988) Not known whether deliberate or accidental, but probably accidental

Risk of Introduction

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T. pisana was the fourth most frequent snail species intercepted by United States quarantine officials between 1993 and 1998, both associated with shipments of goods from the Mediterranean (perhaps especially with tiles) as well as in airline passenger luggage (Robinson, 1999), indicating that it is both accidentally and deliberately transported over long distances, in the latter case probably as a food item, as it is widely consumed in Mediterranean countries (Taylor, 1906-1914; R Cowie, University of Hawaii, personal communication, 2009). Accidental introduction is probably more important than deliberate introduction. It is also readily transported relatively short distances when, for instance, it attaches itself to vehicles (Cowie and Robinson, 2003).

Once introduced, its high rate of growth and reproduction (Cowie, 1984b; Baker, 1986, 2002; Baker and Vogelzang, 1988) and ability to reach extremely high population densities (Basinger, 1927; Gammon, 1943; Mead, 1961; Cowie, 1984c; Baker and Vogelzang, 1988; Baker, 2002) mean that it is a potentially serious and difficult to control pest. It is listed as a potential pest of major concern to the United States (Cowie et al., 2009).

Habitat

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T. pisana is generally considered a species of coastal areas in its Mediterranean and western European range. However, although it is generally most abundant in such areas, it is also found inland, notably in most of Spain, Italy, southwest France and Morocco (Taylor, 1906-1914). Generally its non-agricultural habitat is duneland, dry scrubland, early successional or disturbed habitat, including roadsides, railway banks and human constructs (e.g. Basinger, 1927; Cowie, 1986; Baker and Vogelzang, 1988; Baker and Hawke, 1990; Baker, 1991). It is a species of open, sunny habitats, not of shaded or forest habitat.

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
Terrestrial – ManagedCultivated / agricultural land Secondary/tolerated habitat Harmful (pest or invasive)
Managed forests, plantations and orchards Secondary/tolerated habitat Harmful (pest or invasive)
Managed grasslands (grazing systems) Secondary/tolerated habitat Harmful (pest or invasive)
Disturbed areas Principal habitat Natural
Rail / roadsides Present, no further details Natural
Urban / peri-urban areas Secondary/tolerated habitat Natural
Terrestrial ‑ Natural / Semi-naturalScrub / shrublands Principal habitat Natural
Arid regions Principal habitat Natural
Littoral
Coastal areas Principal habitat Natural
Coastal dunes Principal habitat Natural

Hosts/Species Affected

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The term ‘host’ is rarely used in the pest mollusc literature, in contrast to the entomological literature. This may be because of the lack of specificity exhibited by many snails species in their food preferences (Cowie, 2001a).
 
T. pisana feeds on a number of plants in its natural habitat, many of which might be unexpected to be palatable because of their toughness (Quick, 1952; Cowie, 1982, 1986). However, the distinction between feeding on certain plants and simply using the plants as habitat is not easy to make as there have been no adequate studies of the feeding preferences of T. pisana. There has been some work carried out on the odour attraction of food, in order to inform bait attractants, but no food items tested were found to significantly attract T. pisana (Baker et al., 2012). Some entries in the Host Plants table, derived from Quick (1952), Johnson and Black (1979), Johnson (1980, 1981), Cowie (1982, 1986), and Baker and Hawke (1990), should therefore be treated cautiously. Those listed as wild hosts are only those identified as being fed upon in the literature or from personal experience, and those listed as habitat are simply all plants mentioned (which may be fed upon), with no assessment of significance, as none could be reliably made.
 
Similarly, T. pisana will feed on a wide range of agricultural crops and garden and ornamental plants, as follows.
 
The major crops affected seriously by T. pisana are cereals, citrus and grapevines, as well as pasture. Its major agricultural impacts in Australia (where most work has been done on its ecology and behaviour related to its invasive impacts) became increasingly evident in the 1980s, especially in cereal crops and pasture (Baker, 2002).
 
Most of the information supplied here, especially regarding minor crops affected, comes from Dürr (1946), Godan (1983) and Baker (1986).
 
Cereals. One of the main problems caused by T. pisana and one that has received considerable attention is in Australian cereals (Baker, 1989, 1992, 2002, 2008). Primarily, the problem is that the snails aestivate on the stems and heads of the full grown plants at harvest. Not only does this contaminate the harvested crop, which can result in downgrading of the grain or rejection of bulk shipments of grain overseas, with the associated major economic loss, but it also clogs the harvesting machinery. However, the snails also feed on the crops, including on seedlings of wheat and barley (Baker, 1986, 1989). It is also a cereal pest in South Africa (Joubert and Walters, 1951; Baker, 1986).
 
Pastures. In Australia, legume-based pastures (e.g. annual medics, lucerne, clover) are seriously damaged and occasionally totally destroyed (Baker, 1986, 1989, 2002, 2008). Also, stock reject pasture and hay contaminated with slime trails. In South Africa, T. pisana is also a pest of pasture (Joubert and Walters, 1951; Baker, 1986).
 
Citrus. T. pisana is a pest in citrus orchards in Israel, Libya, other Mediterranean countries, South Africa and in oases in Saudi Arabia (Harpaz and Oseri, 1961; Godan, 1983; Baker, 1986). Damage to citrus was the major concern in California (Gammon, 1943), and remains so should T. pisana become widely established again. It will feed on foliage, bark of tender twigs, fruit and blossoms (Basinger, 1927, quoting de Stefani). Specifically, orange, lemon and grapefruit have been mentioned (Basinger, 1927).
 
Grapevines. Grapevines are attacked in South Africa, Australia and Israel (Dürr, 1946; Baker, 1986; Sanderson and Sirgel, 2002).
 
Vegetables. Vegetables are impacted in South Africa, Israel, in oases in Saudi Arabia, and in most countries where T. pisana occurs (Godan, 1983; Baker, 1986). The list in the Host Plants table is derived primarily from Godan (1983) and Baker (1986). Seed carrots are affected in Australia.
 
Seed lucerne and other legume crops. T. pisana is a problem in seed lucerne in France, where the snails feed on the flowers, the slime inhibits pollination, crushed snails block harvesters, and fouled seeds are unmarketable (Baker, 1986). It is a problem in (unspecified) legume crops in South Africa and Australia (Baker, 1986, 1991).
 
Other crop trees and shrubs. Stone fruit, almonds and olives have been reported to be affected (Baker, 1986, 1988), as have figs (Basinger, 1927). Apples, apricots, peaches and plums were listed by Dürr (1946) but whether these were attacked by T. pisana or by another invasive snail species, Helix aspersa (now known as either Cornu aspersum, Cantareus aspersus or Cryptomphalus aspersus), was not made clear. Oil seed crops (unspecified), including seedlings, are affected in Australia (Baker, 1986).
 
Other. T. pisana is reported as a garden pest and a pest of ornamental flowers and shrubs (Basinger, 1927; Dürr, 1946; Joubert and Walters, 1951; Baker, 1986, 1988).
 
These are the main impacts on particular crops etc. in particular countries that have been reported in the literature. Almost certainly they can be generalized to similar crops in other countries where T. pisana is abundant, but have simply not been reported in the widely accessible literature.

Baker (1989) reported laboratory experiments demonstrating that T. pisana will feed on the following cereal and pasture plants: barley (Hordeum vulgare), wheat (Triticum vulgare), perennial rye grass (Lolium perenne), tall fescue (Festuca arundinacea), cocksfoot (Dactylis glomerata), rape (Brassica napus), vetch (Vicia sativa), clover (Trifolium subterraneum, T. fragiferum), barrel medic (Medicago truncatula) and lucerne (Medicago sativa). It did not feed on phalaris (Phalaris aquatica) and faba bean (Vicia faba).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Acacia (wattles)FabaceaeHabitat/association
Acanthocarpus preissiiAsparagaceaeHabitat/association
Allium cepa (onion)LiliaceaeOther
Aloe (grey alder)AloaceaeHabitat/association
Anthyllis vulnerariaHabitat/association
Apium graveolens (celery)ApiaceaeOther
Asphodelus tenuifolius (onionweed)LiliaceaeHabitat/association
Avena barbata (slender oat)PoaceaeHabitat/association
Avena sativa (oats)PoaceaeOther
Beta vulgaris (beetroot)ChenopodiaceaeOther
Beta vulgaris subsp. maritima (sea beet (UK))ChenopodiaceaeHabitat/association
Brassica oleracea (cabbages, cauliflowers)BrassicaceaeHabitat/association
Brassica oleracea var. botrytis (cauliflower)BrassicaceaeOther
Brassica oleracea var. capitata (cabbage)BrassicaceaeOther
Brassica oleracea var. gemmifera (Brussels sprouts)BrassicaceaeOther
Brassica rapa subsp. rapa (turnip)BrassicaceaeOther
Bromus diandrus (great brome)PoaceaeHabitat/association
Carex (sedges)CyperaceaeHabitat/association
CarpobrotusHabitat/association
Centranthus ruberValerianaceaeHabitat/association
CitrusRutaceaeMain
Convolvulus arvensis (bindweed)ConvolvulaceaeHabitat/association
Crithmum maritimumUmbelliferaeHabitat/association
Daucus carota (carrot)ApiaceaeOther
Dianthus gallicusCaryophyllaceaeHabitat/association
Diplotaxis muralisBrassicaceaeHabitat/association
Eryngium maritimumWild host
Erysimum cheiri (wallflower)BrassicaceaeHabitat/association
Euphorbia balsamiferaEuphorbiaceaeWild host
Fabaceae (leguminous plants)FabaceaeOther
Foeniculum vulgare (fennel)ApiaceaeWild host
GnaphaliumHabitat/association
Hordeum vulgare (barley)PoaceaeMain
Lactuca sativa (lettuce)AsteraceaeOther
Lotus corniculatus (bird's-foot trefoil)FabaceaeHabitat/association
Marrubium (horehound)LamiaceaeHabitat/association
Medicago spp.FabaceaeMain
Olea europaea subsp. europaea (European olive)OleaceaeMain
Olearia axillarisAsteraceaeHabitat/association
Opuntia sp. (pricklypear)CactaceaeWild host
Pelargonium capitatumGeraniaceaeHabitat/association
Pisum sativum (pea)FabaceaeOther
Plantago coronopus (Buck's-horn plantain)PlantaginaceaeHabitat/association
Plantago lanceolata (ribwort plantain)PlantaginaceaeHabitat/association
Prunus dulcis (almond)RosaceaeMain
Raphanus maritimusBrassicaceaeWild host
Raphanus sativus (radish)BrassicaceaeOther
Rapistrum rugosumBrassicaceaeHabitat/association
Reseda lutea (Cutleaf mignonette)ResedaceaeHabitat/association
Rubus (blackberry, raspberry)RosaceaeHabitat/association
Rumex (Dock)PolygonaceaeHabitat/association
Salvia (sage)LamiaceaeWild host
Sedum (stonecrop)CrassulaceaeHabitat/association
Senecio (Groundsel)AsteraceaeHabitat/association
Senecio jacobaea (common ragwort)AsteraceaeHabitat/association
Smyrnium olusatrumApiaceaeWild host
Solanum lycopersicum (tomato)SolanaceaeOther
Thymus vulgaris (thyme)LamiaceaeHabitat/association
Trifolium spp.FabaceaeMain
Triticum (wheat)PoaceaeMain
Umbelliferae (Plants of the parsley family)UmbelliferaeHabitat/association
Urtica dioica (stinging nettle)UrticaceaeHabitat/association
Vitis vinifera (grapevine)VitaceaeMain

Growth Stages

Top of page Flowering stage, Fruiting stage, Post-harvest, Seedling stage, Vegetative growing stage

Symptoms

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Damage is by external feeding and most, if not all above ground parts of the plants are susceptible, perhaps with the exception of bark of well established trees. In most cases the symptoms are obvious – external damage to the plant. Also, the snails congregate on the affected plants in large numbers; their copious slime trails may be especially visible; and, when they leave their resting/aestivation sites on the plants, the remaining dry, white, calcareous epiphragms that they used to seal themselves to the plants may be visible.

List of Symptoms/Signs

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SignLife StagesType
Fruit / external feeding
Growing point / external feeding
Inflorescence / external feeding
Leaves / external feeding
Stems / external feeding
Whole plant / external feeding

Biology and Ecology

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Genetics

There is a huge range of variation in the markings on the shell. Two papers (Cain, 1984; Cowie, 1984a) have been published on the genetic control of the shell patterns, the colour of the shell lip (the edge of the shell aperture) and the colour of the apex (the embryonic shell or protoconch). An earlier paper (Johnson, 1980) investigated the population genetics in introduced Western Australian populations, but without knowledge of the genetic mechanism controlling the variation; a later paper (Hazel and Johnson, 1990) demonstrated an association of frequency of banded versus unbanded shells with habitat and ascribed this to climatic selection (snails with unbanded shells heat up less quickly in sunlight than snails with banded shells). While the phenotypic variation is immense, the control of the patterning seems relatively simple, following the basic rules of Mendelian genetics. The suite of shell patterns seems to differ somewhat from locality to locality, with distinct appearances of Mediterranean and North African shells compared to northwest European shells, although within any one locality the genetics is probably relatively simple. Shell banding pattern has been used to evaluate the origins of introduced populations in California (Cowie, 1987) and of new populations in Wales (Fowles and Cowie, 1989).
 
Only one study has investigated the molecular genetics of T. pisana. Johnson (1988) compared allozyme variation among introduced populations in Western Australia, Victoria and Tasmania (Australia) and southern France, Israel and Wales. He demonstrated that the allelic compositions of the Australian (introduced) samples were consistent with them all having a common source, and that they had the closest similarity to those from southern France, consistent with the original introduction(s) being from this area. Whether there was one or more introductions to Australia and whether the introduction(s) were directly from the ultimate source or from an intermediate introduced population (i.e. in South Africa) could not be determined.
 
Reproductive Biology
 
T. pisana is an obligate cross-fertilizing hermaphrodite. The main publications dealing with its life-history are those of Bonavita and Bonavita (1962), Heller (1982, 2001), Cowie (1984b) and Baker (1991). Compared to other helicid snails, T. pisana is relatively ‘r-selected’ inasmuch as it has a short life span (1-2 years), is semelparous (breeds only over a single season) and produces a large number of small eggs (up to 4566 eggs per pair) (Cowie, 1984b; Baker, 1991). Eggs are laid a centimetre or two below the soil surface in cavities dug out by the snails (Basinger, 1927). Whether it takes one or two years to complete its life cycle depends on environmental conditions, essentially whether it is forced into aestivation for lengthy periods during the summer by hot dry conditions (most Mediterranean habitats) or into hibernation for lengthy periods during the winter by cold conditions (northwest European habitats). Some populations, in both the Mediterranean/European region and in Australia, exhibit mixed one and two year cycles (Baker and Vogelzang, 1988; Baker and Hawke, 1990; Heller, 2001). The differences are not genetic, as snails from naturally annual and biennial populations were annual when bred in the laboratory (Cowie, 1984b). Breeding takes place in summer and early autumn in Britain and northern Europe and in autumn and winter in the Mediterranean and in Australia (Cowie, 1984b; Baker and Hawke, 1990). Cowie (1980a) reported egg-laying when snails were as small as about 10 mm in width, but this has not been reported since and other studies have not found reproductively mature individuals this small (e.g. Cowie, 1984b; Baker and Vogelzang, 1988).
 
Physiology and Behaviour
 
Little is known of the physiology of T. pisana other than in relation to its temperature tolerance and thermal behaviour. The upper lethal temperature for snails from Tenby, south Wales, lies between 42 and 46°C, depending on exposure time (1-8 h), whereas snails from the Mediterranean region (southern Spain) are more tolerant, having an upper lethal limit of 46-50°C; juveniles are more tolerant than adults, and aestivating snails are more tolerant than active ones (Cowie, 1985). The climbing behaviour that is so characteristic of T. pisana (e.g. McQuaid et al., 1979; Heller, 1982; Baker, 1986) seems to be an adaptation to avoiding high temperatures near the ground, which can exceed the lethal limit, especially in its hot Mediterranean range (Cowie, 1985). In the laboratory, adults (at least) avoid the hottest and most exposed (to wind) sides of stems on which they rest (Cowie, 1985). Juveniles in south Wales climb less than adults; with a higher aperture surface area to volume ratio they may be more prone to desiccation than adults and therefore need to remain in the higher humidity near the ground, where their higher temperature tolerance would be advantageous (Cowie, 1985). However, in Australia the opposite is the case, with juveniles off the ground and adults more frequently found on the ground, perhaps because of differences in the microclimatic regimes between the Australian and European habitats (Baker and Vogelzang, 1988). In hotter regions (e.g. the Mediterranean) both adults and juveniles may be forced off the ground. In the northern parts of its range, juvenile snails over-winter in some form of hibernation (adults die before the onset of winter); they do not seem to bury into the ground but congregate in sheltered places such as under overhangs at bases of walls (Cowie, 1984b).
 
Associations
 
Where it occurs, T. pisana is a member of various characteristic land snail faunas. In South Wales, it may be the dominant species of areas very close to the coast (e.g. dunes), in association with much smaller numbers of other snails species including Cornu aspersum (Helix aspersa), Cernuellavirgata, Cochlicella acuta, Ashfordia granulata, Oxychilus draparnaudi, but just a short distance back from the coast (as little as 100 m) it is associated with a slightly different guild of species, viz. Cornu aspersum, Cepaea nemoralis, C. hortensis, Trichia striolata, Candidula intersecta (Cowie, 1982; Cain, 1988). Intermediate areas have a mix of these two groups of species (Fowles and Cowie, 1989). In Mediterranean regions it is again associated with characteristic snail faunas of the coasts, including Otala spp., Eobania vermiculata and various Hygromiidae, and may be transported along with such species, for example in association with domestic tiles (Robinson, 1999). In Australia, T. pisana is associated with other Mediterranean /western European snails as agricultural pests, viz. C.virgata, C.acutaPrietocellabarbara (Baker, 1986, 1989, 2002, 2008; Coupland, 1994, 1995, 1996; Coupland and Baker, 1994, 1995; Coupland et al., 1994).
 
Environmental Requirements

T. pisana is a species primarily of coastal habitats in dry and warm climates. Its characteristic habitat is Mediterranean duneland and disturbed coastal habitats (gardens, agricultural lands, etc), extending to similar duneland and disturbed habitats further north along the western European coasts, but no further north than southwest England and Wales, east-central Ireland and the coast of southern Holland. It has invaded equivalent habitats, primarily those with Mediterranean climates, around the world. While its climatic limits may be constrained by its range of temperature tolerance, whether within those climatic limits it is constrained to such coastal, ruderal habitats by its physiology or by its inability to compete with more ‘K-selected’ species (e.g. Cepaea spp.) that also occur further inland and in more stable habitats is not known (Cowie, 1982). Thus, although it occurs in, for example, some ‘steppe’ habitats, according to the Koeppen classification, it would not be expected to occur in many of the regions of the world that are classified as such as they are distant from a maritime influence. Similarly, it would not be expected to occur in many regions classified as ‘warm temperate’, for both this reason and because higher latitude regions may be too cold. In western Europe, its northern and western limit corresponds roughly with the 5°C isotherm of mean January temperature (Wallén, 1970), although the northernmost French populations and the Belgian and Dutch populations are in cooler regions (Cowie, 1982). The local distribution of T. pisana at Tenby (South Wales) on only south- and west-facing slopes in areas where north- and east-facing slopes appear suitable, indicates the importance that its cold tolerance may have in determining the limits of its range (Cowie, 1984a, 1986). Summer temperatures do not seem to exert control. Probably the southern limit in the Mediterranean and North African region is determined by moisture/rainfall, since a sufficient relatively humid period is required for the life-cycle to progress within one or two years (Cowie, 1984b). On the other hand, its absence from very wet regions that appear warm enough, such as the southwest of Ireland, which has over 250 days of rain per year (HMSO, 1952; Lamb, 1964), may be because it is too wet (Cowie, 1982). Otherwise, insufficient analysis has been undertaken to assess its climatic limits.

Climate

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ClimateStatusDescriptionRemark
BS - Steppe climate Preferred > 430mm and < 860mm annual precipitation
BW - Desert climate Tolerated < 430mm annual precipitation
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Air Temperature

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Parameter Lower limit Upper limit
Mean minimum temperature of coldest month (ºC) 5

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Agama stellio Predator
Anas Predator not specific
Athene noctua Predator not specific
Burhinus oedicnemus Predator not specific Mienis, 1978
Carabus impressus Predator
Coremacera marginata Predator not specific Coupland, 1994; Coupland, 1996; Coupland and Baker, 1995; Coupland et al., 1994
Corvus corone Predator not specific
Crocidura suaveolens Predator not specific
Dichetophora obliterata Predator not specific Anonymous, 1936; Coupland, 1996; Coupland and Baker, 1995
Discomyza incurva Parasite not specific Coupland, 1994
Erinaceus europaeus Predator not specific
Euglandina rosea Predator not specific Barker and Efford, 2004; Cowie, 1997; Cowie, 2001a; Cowie, 2001b; Griffiths et al., 1993
Eumeces schneideri Predator
Eurychaeta muscaria Parasite not specific
Euthycera cribrata Predator not specific Coupland, 1994; Coupland and Baker, 1995
Falco tinnunculus Predator not specific
Fannia canicularis Parasite not specific
Gerbillus andersoni Predator not specific
Gonaxis Predator not specific
Lampyris noctiluca Predator
Melinda caerula Parasite not specific
Melinda cognata Parasite not specific Coupland, 1994
Meriones tristrami Predator not specific
Neoleria Parasite not specific Coupland, 1994
Panagrolaimus Predator/parasite not specific
Phasmarhabditis hermaphrodita Predator/parasite not specific Baker, 2002; Coupland, 1995
Pherbellia cinerella Predator not specific Baker, 2002; Coupland, 1994; Coupland, 1996; Coupland and Baker, 1995; Coupland et al., 1994
Pica pica Predator not specific
Pycnonotus Predator not specific
Rattus rattus Predator not specific
Salticella fasciata Predator not specific Baker, 2002; Coupland, 1994; Coupland, 1996; Coupland et al., 1994; Knutson et al., 1970
Sarcophaga africa Parasite not specific
Sarcophaga anaces not specific
Sarcophaga balanina Parasite not specific Baker, 2008
Sarcophaga carnaria Parasite
Sarcophaga cucullans Parasite not specific
Sarcophaga filia Parasite not specific
Sarcophaga hirticrus Parasite not specific
Sarcophaga maculata not specific
Sarcophaga nigriventris not specific
Sarcophaga portschinskyana not specific
Sarcophaga portschinskyi Parasite
Sarcophaga pumila Parasite not specific
Sarcophaga teretirostris not specific
Sarcophaga unicurva not specific Baker, 2008
Silpha arenaria Predator
Spiniphora maculata Parasite not specific
Testacella Predator not specific
Trypetoptera punctulata Predator not specific Coupland, 1996; Coupland and Baker, 1995
Turdus philomelos Predator not specific
Vanellus spinosus Predator not specific

Notes on Natural Enemies

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The edited volume of Barker (2004) is the major comprehensive source of information. The various chapters that mention T. pisana deal with avian and mammalian predators (Allen, 2004), carabid beetles (Symondson, 2004), Diptera (Coupland and Barker, 2004), other gastropods (Barker and Efford, 2004), reptiles (Laporta-Ferreira and da Graça Salomão, 2004) and nematodes (Morand et al., 2004). The information in the Natural Enemies table comes from these sources, unless otherwise referenced. Although the greatest part of the literature on mollusc-associated Diptera concerns the Sciomyzidae (Coupland and Barker, 2004), there is no mention in Barker (2004) specifically of T. pisana being attacked by sciomyzids; the information provided is derived from Knutson et al. (1970), Coupland (1994, 1996), Coupland et al. (1994), Coupland and Baker (1995), and Baker (2002). The facultative predatory snail Rumina decollata, native to the Mediterranean region, has been used as a biological control agent against T. pisana (Anonymous, 1987), although the author has found no report as to whether the two species interact in their native range (R Cowie, University of Hawaii, USA, personal communication, 2009).

Specifically regarding T. pisana, Charwat, Davies, Coupland, Baker and colleagues have done extensive searches for natural enemies with a view to the possibility of biological control in Australia (e.g. Coupland, 1994, 1995, 1996; Coupland and Baker, 1994, 1995; Coupland et al., 1994; Charwat and Davies, 1997, 1998, 1999).

In many cases, notably concerning insects and nematodes, it has often not been clear whether the “predator” or “parasite/parasitoid” in fact attacks the live snail or whether it feeds on snails that are already dead, or perhaps both. For instance, the sciomyzid fly Salticella fasciata is more of a saprophage than a parasite (Coupland et al., 1994; Baker, 2002).

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)
 
There is no evidence that T. pisana is dispersed via non-biotic natural means, such as the wind, although it is possible that snails, especially small ones (perhaps juvenile T. pisana) can be blown considerable distances by the wind (Kirchner et al., 1997).
 
Natural Dispersal (Biotic)
 
The capacity of T. pisana for active, unaided dispersal is limited, as it is for most snails. In South Africa snails moved on average about 4 m per year (Hickson, 1972) but this was based on movements in isolated patches of vegetation in summer and is probably an underestimate. In Western Australia, during February – July, when increased rain promotes snail activity, the average distance moved by marked snails was about 7 m, although one snail moved 40 m and several moved 20 m or more (Johnson, 1981). In south Wales, over 100 days during the active summer and early autumn season (July – October) no snail moved more than 3 m (Cowie, 1984c). In south Australia, marked snails moved up to 13 m in one week and up to 75 m in three months (Baker, 1988). In most of these studies differences in dispersal rates among habitats were reported (cf. Cowie, 1980b) and may explain, at least in part, the differences among the studies. Only one study has addressed the rate of spread of a newly introduced population of T. pisana (Johnson and Black, 1979), reporting a rate of population expansion of about 20 m per year from 1925 to 1978.
 
Vector Transmission (Biotic)
 
There is no evidence that T. pisana is dispersed via biotic natural means, for instance being carried by other animals, although it is known for other snail species that they can be carried long distances by birds (Ramsden, 1913; Anonymous, 1936; Rees, 1965; Boag, 1986).
 
Accidental Introduction
 
T. pisana has been intercepted in association with numerous plants and plant products entering the United States from Africa (no country specified), Australia, Azores, Bermuda, Canary Islands, Crete, Cyprus, Denmark, England, France, Germany, Greece, Holland, Israel, Italy, Lebanon, Libya, Monaco, Morocco, Poland, Portugal, Spain, South Africa, Turkey and the “United Arab. Republic” [sic] (Godan, 1983). This list of countries includes much of the natural and introduced range of T. pisana, although being on the list does not necessarily mean that the snails themselves originated from and are therefore established in those countries. T. pisana has been intercepted in unspecified cargo entering the United States (Godan, 1983). It has also been intercepted by Canadian authorities on plants and plant products from Malta and Monaco (Godan, 1983). The spread of T. pisana around southern California in the 1930s was in part in association with alfalfa (lucerne) hay that was cut and used as orchard and garden mulch and for other purposes (Hanna, 1966). T. pisana has been found in association with military cargo from Europe (Hanna, 1966). It has been intercepted in luggage, cargo, plant material and postal packages and straw associated with horse equipment, and was introduced (or perhaps just intercepted) to US bases in Germany after World War Two with goods shipped from Morocco and Spain (Godan, 1983). It is one of the species frequently intercepted in shipments of tiles from the Mediterranean to the USA and attached in or on containers, pallets, etc (Robinson, 1999). Its spread in Western Australia has largely been a result of (unspecified) human activity (Johnson and Black, 1979), which could include being accidentally attached to vehicles (Cowie, 1987; Cowie and Robinson, 2003).
 
Intentional Introduction

T. pisana was probably introduced initially to California as a food item (Basinger, 1927; Mead, 1961). It has been intercepted in postal packets entering the United States (Godan, 1983), suggesting a deliberate attempt at introduction. It is widely used as a food item in southern Europe (Taylor, 1906-1914; R Cowie, University of Hawaii, USA, personal communication, 2009), but there seems to be no reason other than this to introduce it deliberately, although Basinger (1927) suggested the slight possibility that it was (perhaps also) introduced by a shell collector; and it was introduced to Guernsey from Jersey for “naturalization” (Taylor, 1906-1914; Barrett, 1972).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Shell collecting. Conjecture Yes Basinger, 1927
Food Yes Basinger, 1927; Mead, 1961
Hitchhiker Yes Yes Cowie, 1987; Robinson, 1999
Horticulture Yes Hanna, 1966
Intentional release Yes Barrett, 1972; Taylor, 1906-1914

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark adults Yes Pest or symptoms usually visible to the naked eye
Bulbs/Tubers/Corms/Rhizomes eggs Yes Pest or symptoms usually visible to the naked eye
Flowers/Inflorescences/Cones/Calyx adults Yes Pest or symptoms usually visible to the naked eye
Fruits (inc. pods) adults Yes Pest or symptoms usually visible to the naked eye
Growing medium accompanying plants eggs Yes Pest or symptoms usually visible to the naked eye
Leaves adults Yes Pest or symptoms usually visible to the naked eye
Roots eggs Yes Pest or symptoms usually visible to the naked eye
Stems (above ground)/Shoots/Trunks/Branches adults Yes Pest or symptoms usually visible to the naked eye
Wood adults Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Seedlings/Micropropagated plants
True seeds (inc. grain)

Wood Packaging

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Wood Packaging liable to carry the pest in trade/transportTimber typeUsed as packing
Solid wood packing material without bark No

Impact Summary

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CategoryImpact
Cultural/amenity Negative
Economic/livelihood Positive and negative
Environment (generally) Negative
Human health Negative

Economic Impact

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T. pisana is widely used as a food item in Mediterranean countries, where it can be found in great numbers in local markets. Huge numbers of the snail were shipped from Europe to California in the early 1900s for food, presumably for sale (Mead, 1961). This appears to be its only positive economic/social value.

Otherwise its impacts, primarily on agriculture, are negative and have been outlined in the section on Crops and Other Plants Affected. Few data on the economic cost or the quantified extent of these impacts are available.
 
In 1984, a shipment of barley from South Australia was rejected by Chile because live snails (Cernuella virgata, though it could easily have been T. pisana) were included with the grain, this one rejected shipment costed the Australian Barley Board AUS $1.3 million (Baker, 1989). Downgrading of barley because of snail contamination can reduce the price paid to farmers from AUS $160 to AUS $120 per tonne (Baker, 2002).
 
In legume-based pastures in Australia, T. pisana reduced herbage yield by 23% in a month, with the clover component reduced by 75% (Baker, 1989), while Baker (1992) reported 83% loss of pasture herbage over two months.

In addition to impacting crops, T. pisana may have other agricultural impacts as it is an intermediate host of nematodes including the lungworm Muellerius capillaris, which is an important parasite of sheep and cattle, although the veterinary significance of these nematodes in Australia are not known (Baker and Vogelzang, 1988; Baker, 1989).

Environmental Impact

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Impact on Habitats 

In South Africa native shrubs are entirely destroyed by the snails, which eat not only the leaves but also the bark of young branches (Dürr, 1946). Otherwise, no natural habitat impacts have been documented, although perhaps only because the focus has been on the agricultural impacts of T. pisana. As a major, abundant component of Mediterranean ecosystems, in which it may or may not be considered native, its importance must be diverse and pervasive, though little studied or documented.
 
Impact on Biodiversity

Competition between introduced T. pisana and native land snails in Israel has been suggested but remains speculative (Heller and Tchernov, 1978). In Australia, the impact of T. pisana on natural ecosystems is essentially unknown, although it will feed on native Australian plants (Baker, 1989) and a native snail species (Bothryembrion melo) has become rare or gone extinct in areas invaded by T. pisana in Western Australia (Baker, 2002). In South Africa it is said to have “exterminated some native species at Cape Town by eating all the available vegetable matter” (Quick, 1952), although which “native species” was not specified.

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Bothriembryon meloNo detailsAustraliaCompetition - monopolizing resourcesBaker, 2002

Social Impact

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As mentioned above, T. pisana is widely used as a food resource in Mediterranean countries and has been shipped to other countries for this reason. However, it can become a public nuisance when it invades urban/suburban areas. The snails crawl up the walls and windows of houses, and in rainy weather it can be difficult to avoid treading on them on sidewalks (Basinger, 1927). Unspecified ‘white snails’ (i.e. T. pisana and/or Cernuella virgata) are intermediate hosts of a fluke (Brachylaima sp.), and young children who have ingested infected snails in South Australia have suffered severe gut disorders (Baker, 2002).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Pioneering in disturbed areas
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Has high genetic variability
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Negatively impacts trade/international relations
Impact mechanisms
  • Competition - monopolizing resources
  • Fouling
  • Herbivory/grazing/browsing
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult/costly to control

Uses List

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Human food and beverage

  • Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)

Diagnosis

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T. pisana is readily identified and distinguished from similar-looking species by simple visual inspection of the shell characteristics.

Detection and Inspection

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Detection is straightforward. Adult snails are normally 15-18 mm in width and readily seen, especially as they tend to rest or aestivate on the plants above the ground during the day and in hot conditions. Juveniles are smaller but are also quite readily seen. Usually population densities are high, making the snails even more readily visible. Detection and inspection is by visual searching. Searching should be focussed on plants, fences, and other vertical surfaces on which the snails rest exposed well above the ground surface, especially in sandy areas. Shipping materials (crates, pallets, containers) coming from areas where the snails are known to exist should be examined. Although generally readily visible, nooks and crannies in containers and shipping materials and cargo should be carefully searched.

Similarities to Other Species/Conditions

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Certain other species of Theba are extremely similar. Distinguishing them is based primarily on the general shape of the shell, whether it is keeled or not, its microsculpture, the structure of the umbilical region of the shell and the shape of the aperture. Identification is best achieved using the key of Gittenberger and Ripken (1987). However, these other species of Theba are rarely intercepted by quarantine officials and seem not to be highly invasive.

The only other species with which it is likely to be confused is the invasive Cernuella virgata (da Costa, 1778), which has a larger umbilicus, deeper sutures, and lacks the spiral striations. Its banding patterns are not as complex as those often exhibited by T. pisana.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

SPS measures
 
In the United States, T. pisana is on a list of actionable pests if detected by quarantine officials, and is one of the species listed as of major concern should it be introduced more widely in the United States (Cowie et al., 2009). The author is not aware of other countries’ regulations regarding T. pisana (R Cowie, University of Hawaii, USA, personal communication, 2009).
 
Rapid response
 
There is no known mechanism currently in place for rapid response to detection of new infestations of T. pisana, although such mechanisms may be in place in the United States. However, despite the problems caused by T. pisana in California in the early twentieth century and the huge effort to eradicate it, when it was rediscovered in 1985 there was some discussion among officials about what to do about the infestations but little action was taken and T. pisana is still present as far as is known (R Cowie, University of Hawaii, USA, personal communication, 2009).
 
Public awareness

In general, the public is almost completely unaware of invasive snails, and this is probably largely true regarding T. pisana despite the extreme abundances it may reach. Awareness may be greater in Australia since it has a significant economic impact, notably on cereal agriculture, and may generate more news stories than other pest snails/slugs. In particular, T. pisana, along with a number of other exotic species in Australia, has significant localised pest status.  
 
Eradication
 
Eradication has been reported in California (Armitage, 1949), some 35 years after the initial introductions. The final resort was the use of flame throwers, which were able to penetrate the nooks and crannies that simply setting fire to the vegetation could not. Hand picking was considered essential in order to find the last remaining individuals (Basinger, 1927). Use of calcium arsenate bait was also used extensively as part of the eradication campaign (Basinger, 1927). Whether eradication was completely successful is open to debate, since T. pisana was discovered again in the 1960s (supposedly eradicated again) and again in 1985, when fire was used in attempts to eradicate them (Anonymous, 1987). As for most snails, eradication is extremely difficult, since in general the snails (as is the case for most invertebrate species) are well established and locally widespread before people become sufficiently aware of them to complain or report that there is something new in their environment that may be causing a problem. Confirming that every last snail has been killed is extremely difficult.
 
Control
 
Baker (1986, 2002) described the various control measures that have been implemented or considered in Australia. The following is taken from those sources unless otherwise referenced.
 
Cultural control and sanitary measures
 
Windrowing (cutting the cereal stalks before the grain is ripe, raking the crop into rows and leaving it to ripen on the ground) can reduce contamination of the grain because the snails tend to aestivate on the stubble between the rows. Burning and tilling prior to sowing has been used to kill snails, but is used less so because of soil conservation concerns (Leonard et al., 2003). Also, fire may not burn evenly across an area and some snails may remain unburned. Burning has been recommended in South Africa (Joubert and Walters, 1951), and removal of vegetation, followed by use of flame throwers has been carried out in California (Basinger, 1927). Intensive grazing and control of tall weeds (that provide aestivation sites) may reduce snail numbers, but may also encourage the snails to move from the pasture to an adjacent crop. Clearing the edges of fields after harvest of lucerne in France was also deemed useful (Godan, 1983). Maintaining open and weed-free areas around fences has also been encouraged in Australia as it helps to reduce the probability of snail breeding grounds (Leonard et al., 2003). Spraying snails with hot water kills them, but the length of time they need to be sprayed is too long and the water also kills plants (Basinger, 1927). Hand collecting has also been recommended in South Africa (Joubert and Walters, 1951).
 
Physical/mechanical control
 
Outriggers have been used on harvest machinery to knock aestivating snails off the infested cereal plants, but they tend to dislodge the grain as well as the snails. Some farmers drag chains or iron bars across fields to dislodge aestivating snails, which then die from exposure to high temperatures on the ground surface. Others use heavy rollers to crush the snails but this is only effective if the ground is hard and flat (Leonard et al., 2003).
 
Movement control
 
Baker (2002) suggested that concentrated ‘barriers’ of molluscicide might be deployed along fence-lines to prevent snail invasions into crops.
 
Biological control
 
The generalist predatory snails Euglandina rosea (from Florida) and Gonaxis sp. (from Kenya) have been introduced to South Africa for biocontrol of T. pisana but neither of them became established (Barker and Efford, 2004). The facultative predatory snail Rumina decollata was said to be able to control but not eradicate T. pisana in California (Anonymous, 1987), although the efficacy of R. decollata has been questioned (Cowie, 2001a). Extensive screening of Diptera, notably Sarcophagidae and Sciomyzidae, and some nematodes as biocontrol agents has taken place with a goal to control T. pisana in Australian agriculture (see section on Natural Enemies). However, no species has been introduced specifically to control T. pisana because those screened were either ineffective or attacked non-target snails, including native Australian species, and no biological control agents were being considered for release against T. pisana in Australia as of 2008 (Baker, 2008). Ducks were recommended by Joubert and Walters (1951) for small scale control of T. pisana in South Africa.
 
Chemical control
 
In California, various chemicals were tested experimentally against T. pisana, although during the eradication campaign only calcium arsenate was deployed (Basinger, 1927). Calcium arsenate was also considered effective in South Africa (Joubert and Walters, 1951); methiocarb and carbaryl have also been recommended for use in South Africa. Many other chemicals are available in a range of formulations (Godan, 1983; Bowen and Antoine, 1995). In Australia, the widely used molluscicide metaldehyde, in bait formulations, has been traditionally broadcast against T. pisana but is expensive and may have non-target impacts.
 
Various fumigants have also been tried in order to kill T. pisana in shipments of goods and in grain silos but high doses and longer periods of treatment than for insect control proved necessary (Godan, 1983; Baker, 2002).
 
Control by utilization
 
The only use of T. pisana is as human food, in the Mediterranean and possibly in emigrant Mediterranean communities in other countries (the reason for its original import to California). The potential market is far too small to result in significant control.
 
Monitoring and Surveillance

Grain growers in Australia are encouraged to use quadrats and other sampling methods to monitor snail abundance, and to integrate monitoring into their routine checks. Control measures can then be directed according to information on the species of snail present, the number of different species, the size (life cycle stage) and which areas of the paddock have the highest abundance of snails (Leonard et al., 2003).     

It is possible that in California, T. pisana is monitored in case it should spread further.

Gaps in Knowledge/Research Needs

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It is not known whether T. pisana should be considered native or not around much of the Mediterranean and western Europe. Even if it invaded much of the region post-glacially, it should still be considered native if that spread was not aided by people. However, in some instances introduction may have been by people, either accidentally or deliberately. Detailed investigation of the Holocene palaeontological record at numerous localities within this range would shed great insight into the history of the spread of this species.

References

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Mead A R, 1971. Helicid land mollusks introduced into North America. Biologist. 104-111.

Peile A J, 1926. The Mollusca of Bermuda. Proceedings of the Malacological Society of London. 71-98.

Pennant T, 1777. British zoology. London, UK: Benjamin White. vii + 136 pp.

Quick H E, 1952. Emigrant British snails. Proceedings of the Malacological Sciety of London. 181-189.

Quick H W, 1953. Helicellids introduced to Australia. Proceedings of the Malacological Society of London. 74-79.

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Links to Websites

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WebsiteURLComment
CSIRO Entomologyhttp://www.csiro.au/org/Entomology.html
Featured Creatures - white garden snailhttp://entnemdept.ufl.edu/creatures/misc/white_garden_snail.htm
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.
North American Plant Protection Organizationhttp://www.pestalert.org

Contributors

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27/08/09 Original text by:

Rob Cowie, Consultant, Hawaii, USA

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