Cornu aspersum
(common garden snail)

Pictures

Picture	Title	Caption	Copyright
Title Adult Caption Cornu aspersum (common snail, garden snail); adult, extended and moving. Mandaio, Oza dos Rios, Galicia, Spain. May, 2006. Copyright ©Luis Miguel Bugallo Sánchez - CC BY-SA 2.5 ES	Adult	Cornu aspersum (common snail, garden snail); adult, extended and moving. Mandaio, Oza dos Rios, Galicia, Spain. May, 2006.	©Luis Miguel Bugallo Sánchez - CC BY-SA 2.5 ES
Title Adult shells Caption Cornu aspersum (common snail, garden snail); adult shells. Rare sinistral form (a) and common dextral form (b). Haute-Garonne, France. December, 2012. Copyright ©Didier Descouens/Muséum de Toulouse/via wikipedia - CC BY-SA 4.0	Adult shells	Cornu aspersum (common snail, garden snail); adult shells. Rare sinistral form (a) and common dextral form (b). Haute-Garonne, France. December, 2012.	©Didier Descouens/Muséum de Toulouse/via wikipedia - CC BY-SA 4.0
Title Adults Caption Cornu aspersum (common snail, garden snail); adults mating. Copyright ©Ian Dunster/via wikipedia - CC BY-SA 3.0	Adults	Cornu aspersum (common snail, garden snail); adults mating.	©Ian Dunster/via wikipedia - CC BY-SA 3.0

Identity

Preferred Scientific Name

• Cornu aspersum Müller

Preferred Common Name

• common garden snail

Other Scientific Names

• Acavus (Helix) adspersa
• Cantareus aspersus (Müller, 1774)
• Cochlea vulgaris (da Costa, 1778)
• Coenatoria aspersa (Müller, 1774) Held, 1837
• Cornu aspersum aspersum (Müller, 1774)
• Cornu copiae Born, 1778
• Cryptomphalus aspersus (Müller, 1774)
• Helix (Acavus) aspersa Müller, 1774 - Gray, 1840
• Helix (Cryptomphalus) aspersus (Müller, 1774) – Moquin-Tandon, 1855
• Helix (Helicogena) aspersa Férussac, 1821
• Helix (Pentatoenia) aspersa
• Helix (Pomatia) adspersa
• Helix (Pomatia) fluminensis
• Helix adspersa
• Helix aspera
• Helix aspersa Müller, 1774
• Helix depressa Paulucci, 1879
• Helix lucorum Razoumowsky, 1789
• Helix minor Paulucci, 1879
• Helix rufescens
• Helix secunda
• Helix solidissima Paulucci, 1879
• Helix spumosa Lowe, 1861
• Helix variegata Gmelin 1789
• Pomatia aspersa Tryon, 1866

International Common Names

• English: brown garden snail; brown snail; common garden snail; common snail; European brown snail; European brown vineyard snail
• Spanish: caracol comun; caracol de jardin; caracol manchado de las vinas
• French: cagouille; cararaulada; carareu; carsaulada; chagrine; escargot du jardin; escargot petit-gris; griset; helice chagrin; luma; petit-gris

Local Common Names

• Austria: Weitmündige Weinbergschnecke
• Belgium: Blond des Flandres
• Czech Republic: helmýzd kropenatý
• Denmark: plettet voldsnegl
• France: escargot chagrine; gros gris; la zigrinata; limat
• Germany: Gefleckte Weinbergschneke; Gesprenkelte Schnirkel-schnecke; Schnecke, Gefleckte Weinberg-
• Italy: bavalassa; caracoi; castruni; cazzavone; cervone; chiocciola corrugata; chiocciola grigia; ciammaruco; cornacola; elice aspersa; marruco; maruzza; maruzza trapanese; sauru
• Malta: ghakrux ragel
• Netherlands: kleine wijngaardslak; segrijnslak
• South Africa: bruinslak
• Spain: caracolas
• UK: garden snail; small grey snail

EPPO code

• HELXAS (Helix aspersa)
• HELXLU (Helix lucorum)

Summary of Invasiveness

C. aspersum, the common garden snail, is represented by several forms that are highly differentiated genetically. Only one lineage, the western one, is considered to be invasive in regions where it has been introduced recently (since the sixteenth century) either accidentally or intentionally (e.g. North and South America, South Africa, Oceania). It was in California, USA, where it was introduced in the 1850s, that it was first treated (1931) as a regulated pest. Its success in colonizing new areas after introduction and establishment may be due to: (i) large phenotypic variation in combinations of life-history traits, especially reflecting a high degree of plasticity (e.g. trade-off of egg weight/egg number), and (ii) great resistance against natural enemies. Also, genetic data indicate that C. aspersum is capable of establishing even after a severe genetic bottleneck.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

Cornu aspersum (Müller, 1774) is the single species in the genus Cornu Born, 1778. The family Helicidae Rafinesque, 1815 groups 17 genera of large snails with mainly globular shells, including the well known Helix, Cepaea and Arianta. Many of them are eaten by people and some are reared for consumption (e.g. Cornu aspersum, Helix pomatia, Helix lucorum, Otala punctata, Theba pisana, Iberus gualterianus alonensis). Cornu aspersum is highly variable morphologically and several distinct morphotypes have been described, relating to size, shape, thickness and colour of the shell. The form maxima has been distinguished by some authors as a distinct subspecies C. aspersa maximum (Taylor, 1914), known in French as 'gros-gris', with C. aspersum sensu stricto known as the 'petit-gris' (see pictures). However, the status of C. a. maximum as a valid subspecies is not well supported (e.g. Guiller et al., 2001).

The generic name for C. aspersum has been a source of controversy for some time (Cowie, 2011; ICZN, 2015). The species was first described by Müller (1774) as Helix aspersa (meaning “spotted” snail in reference to the shell patterning). Born (1778) gave the name Cornu copiae to a scalariform specimen of the species (one with the shell coils not abutting). The genus Helix is now widely considered inappropriate for the species because of differences in the structure of the reproductive apparatus. Two alternatives to Cornu have been circulating in the literature: Cryptomphalus (Charpentier, 1837) and Cantareus (Risso, 1826). Cryptomphalus is generally considered invalid as a younger synonym of Cornu (if the latter is treated as a nomenclaturally available name), and the use of Cantareus is still not accepted by the majority of malacologists. However, Cornu has been considered unavailable by some scientists, as they have considered that the International Code of Zoological Nomenclature (ICZN, 1999), Article 1.3.2. excludes names based on teratological specimens. However, the recent trend among malacologists has been to consider the name Cornu as nomenclaturally available (e.g. Falkner et al., 2001; Anderson, 2005). The issue was resolved in 2015 by Opinion 2354 of the International Commission on Zoological Nomenclature (ICZN, 2015), which, in response to an application by Cowie (2011), ruled under Articles 78.2.3 and 80.2.1 that the wording of Article 1.3.2 be interpreted to confirm the nomenclatural availability of Cornu Born, 1778 for a genus of land snails (family Helicidae), that was based on a teratological specimen of Helix aspersa Müller, 1774. Thus the correct name for the species is now Cornu aspersum (Müller, 1774).

Description

C. aspersum is a large-sized land snail, with a shell generally globular but sometimes more conical (higher spired) and rather thin in the common form when compared to other Helicinae. The umbilicus is usually completely closed by a thickened white reflected lip that defines the peristome in adult snails. The shell is sculptured with fine wrinkles and rather coarse and regular growth-ridges and is moderately glossy because of a fine periostracum. The peristome is roundly lunate to ovate-lunate. Adult shells (4½ to 5 slightly convex whorls) measure 28-45 mm in diameter, 25-35 mm in height (Kerney and Cameron, 1979). The shell ground colour is from yellowish to pale brown. The shell also shows from zero to five reddish brown to blackish spiral bands superimposed on the ground colour and usually interrupted such that the ground colour appears as yellow flecks or streaks breaking up the bands; the bands are occasionally separated by a median white spiral line (fascia albata). Fusion of two or more adjacent bands and diffusion of band pigment on the whole shell surface are often observed. Frequently, the upper half of the shell is darker because of the effect of a dominant factor (Albuquerque de Matos, 1985). The banding pattern is much less distinct and more broken than that exhibited by the well-known polymorphic snails Cepaea nemoralis and Cepaea hortensis.

The head and foot are 5-10 cm long when extended, yellowish-grey to greenish-black, often with a pale line along the back from the base of the tentacles to the shell. Specimens with soft parts entirely dark are occasionally observed.

Eggs

Eggs are laid in clutches in hollows up to 7 cm below the soil surface dug out by the snail and covered with earth. Clutches vary in number of eggs from about 40 to 100 that are clustered together and joined by a sticky, colourless mucus. They are roundish-oval in shape, roughly 4.25 mm long by 4 mm wide. The eggs are encased in a membraneous cuticle composed of several concentric layers or films and a whitish, thinly calcified shell.

Juveniles

Newly-hatched juvenile shells, which are fragile and translucent, lack any pattern of shell bands and flecks. However, as they grow the shells rapidly become coloured. The shell colour and pattern polymorphism is better observed in young individuals because the periostracum tends to become darker in adults. Old individuals are easily recognized because some parts of the periostracum become worn, exposing the underlying calcified shell. In natural populations, formation of a reflected lip round the shell aperture indicates sexual maturity and the end of somatic growth. Two juvenile classes are distinguished by snail farmers for practical reasons (Daguzan, 1982), based on shell diameter (D), i.e. first stage juveniles with D < 22 mm and second stage juveniles with D > 22 mm.

Distribution

C. aspersum has long been the subject of extensive studies that have led to the recognition of several endemic forms (Taylor, 1914). Whilst the origin of the one form considered distinct, i.e. the farm reared 'gros-gris' or form maxima, is doubtful because its range is currently unknown, the other common form, aspersa sensu stricto, is probably native to North Africa (Taylor, 1914) where genetic discontinuities indicate differentiation of well-defined eastern and western lineages (Guiller et al., 1994, 1998, 2001, 2006). The western lineage would have then expanded from north Africa to Europe via both the Tyrrhenian route and the Straits of Gibraltar (Guiller and Madec, 2010). Historical events involving vicariant and dispersal processes would explain the 'east-west' genetic split and the northward expansion of the western clade. The distribution essentially reflects both Pliocene/Pleistocene climatic changes and Tertiary geomorphological events.

Nowadays, the western lineage of C. aspersum has become a typically anthropochorous form widespread throughout the world in many regions having Mediterranean, temperate and even subtropical climates. Its presence is now reported in North and South America and Africa, as well as in the Mascarene Islands, Oceania and Asia. Much more recent events related to human activities are undoubtedly responsible for such longer distance dispersal. The subject of farming since the Roman age, the western form has successfully colonized a large range of landscapes disturbed by humans (agricultural, urban and suburban areas), and it is considered an important agricultural and garden pest in lands where it has been recently introduced and naturalized (Barker, 2002).

In Canada, C. aspersum was recorded in the 1850s in Nova Scotia (Taylor, 1914) but has not been found there since (Grimm et al., 2009). It was recorded in the 1970s in Newfoundland but whether it persists there is not known (Grimm et al., 2009). There have been sporadic records around Vancouver and on Vancouver Island, and at present in Canada C. aspersum can only be considered to occur, but not to flourish, around Victoria (Grimm et al., 2009).

Distribution Table

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.

History of Introduction and Spread

C. aspersum has been disseminated to many parts of the world (i) intentionally as a human food source (both as an inexpensive protein source for local consumption and for the gourmet restaurant trade), (ii) accidentally associated with the movement of plants, (iii) and by hobbyists who collect snails (see Pictures). It is also occasionally considered as a domestic pet. Recently, this snail has gained popularity as the main ingredient in skin nutritive creams and gels (crema/gel de caracol) used for getting rid of wrinkles, scars, dry skin and acne.

In some northeast European countries, e.g. Austria, the species has been introduced with vegetables (Reischütz, 2002). In North America, it was introduced into California in the 1850s as a source of 'escargot' by a Frenchman who intended to sell it as food (Forbes, 1850). However, the market during the Gold Rush was too unsophisticated for snails, and he ended up dumping some snails, and others escaped. Other snails were intentionally introduced from France into several areas of California between 1850 and 1860 (Stearns, 1900). By 1900, C. aspersum was present throughout much of the agricultural areas of California and it has been regarded as a pest in citrus since that time (Basinger, 1931). Other sources indicate that the species was recorded in 1839 in Portland (Maine), in New Orleans (Louisiana, introduced from Spain) and in Massachusetts (introduced from Ireland). In Central and South America, Spanish colonization (from the sixteenth century) may have been responsible for its introduction, for example to Haiti and Chile. It was also imported to Colombia (Bogota) from Brazilian stock for farming purposes in the 1970s (Hausdorf, 2002). However, the project failed and the snails dispersed widely.

In regions of Africa where C. aspersum is not native, it may also have been introduced for human consumption, e.g. to South Africa, with the first record in 1855 in Cape Town (DG Herbert, Natal Museum, South Africa, personal communication, 2009). However, Herbert suggested that C. aspersum was probably introduced accidentally long before this, perhaps around 1650-1700. As other European helicids, C. aspersum, especially the maxima form has been introduced recently to Israel for food (Roll et al., 2008). Originally from Italy, it would have been imported for promoting new helicicultural opportunities. Originally present in snail farms, both forms (aspersa, maxima) can now be found in various habitats such as parks and gardens throughout the country. They are considered as regulated pests.

In the Mascarene Islands, traders of the French East India Company (beginning in the seventeenth century) were involved in the introduction of C. aspersum, especially to La Réunion, as animal feed (Madec, 1989 ).

In the Pacific, C. aspersum was introduced to some islands deliberately for culture (Cowie, 2000). The oldest introduction was to New Caledonia in 1879 (Gargominy et al., 1996). In New Zealand, C. aspersum is particularly common in coastal scrubland and dune systems of northern New Zealand, both on the mainland and on many islands (Barker, 1999; Brook, 2000). Some people have suggested that the species was deliberately introduced by the French for food. In the Hawaiian Islands, C. aspersum was first recorded on the islands of Oahu in 1952 (Kondo, 1956; Cowie, 1996, 1997), Kauai in 1965 and 1976 (Nakahara, 1979), Hawaii in 1976 (Tamura et al., 1981) and Maui in 1981 (Tamura et al., 1981). In French Polynesia, it was recorded in Tahiti by Solem (1964). Barker (1999) reported the species on Pitcairn and Easter Islands. In 2002 C. aspersum was intercepted on the Pacific island of Niue on containers from New Zealand, and in 2006 in Samoa and Fiji on containers from New Zealand and on wooden pallets (no origin specified), respectively (PESTNET, 2015).

In Asia, a branch of the Chinese Academy of Sciences introduced the species to China from France in the early 1980s (W Wang, Pharmacom Corporation, Iowa, USA, personal communication, 2009). Around the middle of the 1990s, a company in northern China commercialized the technology of snail farming and management in Hebei Province. The 'meat' was mainly used as food at Chinese dining tables. From 2008, a US-based biotech company started to extract and purify the functional contents of the snail for skincare products and medical applications.

Introductions

Risk of Introduction

C. aspersum is farm-raised in several countries where it has been introduced intentionally (eastern Europe, South America, Asia, etc.) as a source of food and skin care products. Countries, especially east European, south American and Asian ones, importing snails either live, fresh, frozen or canned, propose now to augment their economies through development of snail farming and the promotion of processed snail meat products on the world market. The promise that specific ingredients of the snail secretion give a rejuvenating appearance to the skin have led to increased deliberate introductions as some specific creams marketed since 1995 in Chile are now commercialized in 35 countries. C. aspersum is a quarantine plant pest in various states in the USA (Arizona, California, Louisiana, Oregon, South Carolina and Washington) and in Canada.

Habitat

Habitat List

Hosts/Species Affected

C. aspersum is a polyphagous grazer with a large diet spectrum. In its natural habitat, it feeds on wild plants such as Urtica dioica or Hedera helix, which are also used for shelter. In human-disturbed habitats, a wide range of crops and ornamental plants are reported as hosts: these include vegetables, cereals, flowers and shrubs (Godan, 1983; Dekle and Fasulo, 2001). In particular, it causes serious damage in citrus groves and vineyards. It will feed on both living and dead or senescent plant material. The Host Plants/Plants Affected table does not cover all plants that C. aspersum will feed on, as the list is so extensive but aims to provide an insight to the well-known species affected. The categorization as 'Main', 'Other' or 'Wild host' is also subjective and should not be considered definitive.

Growth Stages

Symptoms

C. aspersum causes extensive damage in orchards (creating holes in fruit and leaves) and to vegetable crops, garden flowers and cereals.

In California, USA, populations established in citrus groves feed essentially on the foliage of young citrus and also on ripe fruits, creating small holes allowing the entry of fungi and decay of the fruit (see Pictures). Larger holes result in fruit dropping from the tree or being rejected for consumption during sorting and packing (Reuther et al., 1989; Sakovich, 2002).

In South African viticultural regions, C. aspersum feeds essentially on the developing foliar buds and young leaves of the vines. In kiwifruit vineyards (California, New Zealand), damage occurs on the flowers, not the fully developed fruit, since snails consume only the sepal tissue around the receptacle area. Damage to the sepals can be detrimental by increasing the development of the fungus Botrytis cinerea during cold storage of fruits, and moreover, the slime trail mucus stimulates germination of B. cinerea conidia (Michailides and Elmer, 2000).

List of Symptoms/Signs

Biology and Ecology

Genetics

Extensive work has been carried out on the population genetics of C. aspersum in its native range. There is a clear pattern in geographical structure in North Africa with a west versus east pattern of variation for all the polymorphisms considered (Guiller et al., 1994, 1996, 1998, 2006; Madec and Guiller, 1994; Madec et al., 1996, 2003; Guiller and Madec, 2010). This divergence becomes still more apparent when European populations are considered because of their clustering with those of western North Africa. Moreover, the great genetic diversity in North Africa contrasts with the smaller genetic divergence between populations in Europe.

A study using mtDNA and microsatellite markers (Hiraux, 2009) showed that invasive populations (from California and New Zealand) contained mixtures of haplotypes from different European source populations (indicating multiple introductions) and, as a result, exhibited increased genetic diversity.

As noted above, C. aspersum is a highly variable species. Two forms (considered by some authors to be valid subspecies), i.e. C. aspersum sensu stricto and the form maxima, are relatively well known and both are reared in French snail farms. Molecular markers showed strong genetic divergence between the two forms (Guiller et al., 2001) and the consideration of the standard anatomical criteria used for diagnosis of pulmonate species (Solem, 1978) suggested that the variation in distal genitalia could lead to precopulatory reproductive isolation (Madec and Guiller, 1993, 1994). However, successful experimental interbreeding showed that egg development and hybrid fertility seem not to be altered (Chevallier, 1980). Moreover, some breeders also market giant varieties they have selected for shell ground colour (e.g. ‘blond des Flandres’ with a yellow shell without any bands).

The number of chromosomes and chiasma frequencies seem variable. Karyotype analysis gave counts of 48, 50 or 52 chromosomes (Rainer, 1968). However, no differences between the two forms were observed by Madec (1989a) who reported a haploid number of 27 and the same high chiasma frequencies.

In relation to snail farming performance, experiments including quantitative genetics of life history traits of C. aspersum (form aspersa) led to estimates of genetic parameters for adult weight, growth and reproductive traits (Dupont-Nivet et al., 1997, 1998). Metabolic scaling in fast- versus slow-growth phases of non-selected lines versus lines artificially selected for increased size has also been investigated (Czarnoleski et al., 2008).

Reproductive Biology

Hermaphroditism is universal among pulmonate gastropods. The reproductive biology of C. aspersum, with special reference to mating behaviour and physiology, has been studied in detail by Giusti and Lepri (1980), Tompa (1984), Chung (1987) and Adamo and Chase (1988, 1990). C. aspersum is an obligate out-crossing species. A mature snail mates from 2 to 6 times in a single season and mating requires 4 to 12 hours. Both members of the pair act simultaneously as male and female. Thus, both animals receive sperm in very large numbers (each ejaculate contains about 5.5 x 10⁶) in every mating. A spermatophore is used to package the sperm and thereby protect them during transfer. The reproductive behaviour of C. aspersum exhibits several features, including multiple mating, long-term sperm storage, allosperm digestion, internal fertilization and dart shooting, that may promote sperm competition. The role of dart shooting and the related mucus gland in sperm competition has been extensively studied in C. aspersum (Rogers and Chase, 2001; Chase and Blanchard, 2006; Chase and Vaga, 2006; Chase and Darbison, 2008).

C. aspersum is oviparous, meaning that fertilized eggs are encapsulated in a partially calcareous shell and are laid with little or no embryonic development. The snails deposit white spherical or oval eggs about 3-5 mm in diameter in a cavity 4-7 cm deep that the snail has dug out of moist, loose soil with its foot. The egg mass is concealed by a mixture of soil and secreted mucus followed by a faecal ribbon in contact with the clutch and the nest is covered with soil. Oviposition occurs about 2 weeks after fertilization and its duration is from 10 to 35 hours. Snails from natural populations lay eggs two or three times per season for at least 2 years (C. aspersum is iteroparous), with egg numbers per clutch ranging from 70-80 (dwarfs from sub-tropical islands) to 200-220 for the large form maxima, averaging 100-120 (Madec and Daguzan, 1993; Madec et al., 1998, 2000). According to the pioneering work of Basinger (1931) on a population in California, each individual is capable of laying about 86 eggs once every 6 weeks from February to October, so that approximately five ovipositions are made each year and 430 eggs laid. Numerous data showing the variation in fecundity and reproductive output under artificial conditions are also available because the species is the principal subject of heliciculture (Daguzan, 1982, 1985; Stephanou, 1986; Elmslie, 1989).

Mating and oviposition frequencies are influenced by abiotic (temperature, photoperiod, humidity, soil conditions) and biotic (crowding) pressures (Dan and Bailey, 1982; Lucarz and Gomot, 1985). Low temperature and low humidity inhibit the activity of the snails, and dry soil is unsuitable for ovipositing. During warm damp weather, oviposition may be as frequent as once a month.

During the summer, the eggs hatch in about two weeks but the time to hatching varies from 14 to 40 days according to the environmental relative humidity (Guéméné and Daguzan, 1983). Egg cannibalism by hatchlings is frequent: 70% of new-born snails, which remain in the soil cavity for several days, ingested one sibling egg during their first 4 days of life, facilitated by high hatching asynchrony within the clutch (Elmslie, 1988).

Maturity requires about 2 years in natural populations, with the snails attaining a diameter of 16-20 mm within the first year, and 26-33 mm by the second year in North Africa; 3 or more years are needed for the larger form maxima. In many human-modified areas where snail activity is not interrupted by aestivation or hibernation (parts of South Africa, New Zealand, Mediterranean Europe, California), the snails take about 10-12 months to become mature, producing one generation a year (Potts, 1972; Albuquerque de Matos and Corto-Real, 1994; Sakovich, 2002). In artificial conditions optimized for growth, the recurved lip often appears after three months, but this does not coincide with reproductive maturity.

As for reproductive traits, many environmental factors, abiotic (temperature, humidity, photoperiod) and biotic (density, maternal effects), influence the growth rate and the trade-off of age versus size at maturity. Thus, long days are an ultimate environmental cue stimulating growth and egg-laying whereas short days inhibit them (Bailey, 1981; Enée et al., 1982; Le Guhennec, 1986). In artificial conditions, growth rate is influenced by both food availability and conspecific crowding (Cowie and Cain, 1983).

Physiology and Phenology

Being an ectothermic animal, C. aspersum is active only when external conditions are favourable. Its wide distribution leads to geographic variation in annual activity rhythms, with differences related to latitude and microclimate (Madec and Daguzan, 1993; Iglesias et al., 1996). This species is characterized by considerable plasticity in its responses to environmental differences. Thus, the breeding season is restricted to spring and summer in northern localities, to autumn or even winter in the Mediterranean area (Chevallier, 1983). Sacchi (1971) suggested that reproduction is potentially continuous and might occur during all sufficiently wet and warm periods of the year, as supposed for populations in La Réunion (Madec and Daguzan, 1993). Periods of activity are followed in higher latitudes by hibernation, which has a diapause value (Bailey, 1983; Lorvelec and Daguzan, 1990), and in lower latitudes by aestivation, which in some cases is only a warm torpor. Overwintering in C. aspersum lasts more than 7 months in Scotland (Crook, 1980), 6 months in Wales (Bailey, 1981), approximately 5 months in northwestern France (Lorvelec and Daguzan, 1990) and 4 months in northwestern Spain (Iglesias et al., 1996), while some Mediterranean populations do not hibernate (Madec, 1989a). Cessation of activity is influenced by photoperiod, temperature and humidity, the relative importance of which depends on latitude and local conditions (Jeppesen and Nygard, 1976; Jeppesen, 1977; Bailey, 1981; Bailey and Lazaridou-Dimitriadou, 1986; Lazaridou-Dimitriadou and Saunders, 1986; Aupinel, 1987).

During dormancy, snails bury in the soil or crawl into crevices among rocks, retire into their shells and produce a calcareous and mucous epiphragm sealing the shell aperture (Barnhart, 1983). Their metabolic rate is depressed to 5-30% of its normal value (Herreid, 1977; Barnhart and MacMahon, 1987; Storey and Storey, 1990; Brooks and Storey, 1997): oxygen consumption, water exchange, heart rate, neural activity and patterns of protein synthesis and activation are modified (Machin, 1966, 1972; Riddle, 1983; Barnhart and MacMahon, 1987; Bailey and Lazaridou-Dimitriadou, 1991; Biannic et al., 1994; Brooks and Storey, 1995, 1997; Feneglio et al.,1997; Pakay et al., 2002). A moderately enhanced cold hardiness is related to hibernation, allowing the snails to bear temperatures as low as c. –5°C (Ansart et al., 2001). However, young individuals seem unable to really hibernate and thus exhibit higher mortality during overwintering (Charrier, 1980; Biannic, 1995).

During active periods, activity occurs mainly at night, when temperature declines and humidity is enhanced. Bailey (1975) and Lorvelec et al. (1991) described two peaks of activity, approximately 2 and 6 hours after sunset. During the day, locomotor activity is restricted to periods of rainfall (Biannic et al., 1995).

Longevity

Precise estimates of the longevity of C. aspersum are not available. Observations in natural conditions indicate a life span of 3-5 years but the species is known to live up to 10 years in artificial conditions (Taylor, 1914; Comfort, 1957). Indirect observations (growth breaks and inner layers of shell peristome) show that giant individuals collected from natural populations in North Africa have a longer life expectancy (>10 years).

Nutrition

Having rasping mouthparts (radula), C. aspersum is a polyphagous grazer with a large diet spectrum. Its enzymatic complement allows degradation of cellulose, hemicellulose and xylane, and its gut microflora enhances digestive abilities (Charrier and Rouland, 1992; Charrier et al., 1998, 2000). It preferentially selects green living plants but is also reported to graze on flowers and fruits. It can also eat dead animal tissue and paper products.

Feeding activity is essentially nocturnal and occurs only when relative humidity is sufficient, around 80% (Gallois, 1983). In the laboratory, feeding behaviour is very plastic and sensitive to conditioning (Desbuquois and Daguzan, 1995). Although field observations are scarce, the diversity of the snails’ diet varies quantitatively and qualitatively with the season and availability of plants, and the snails do not eat at random (Iglesias and Castillejo, 1999). Pulmonate snails use distance chemoreception and taste to realise their choices, feeding preferences being influenced by the biochemical composition of the plants and especially by secondary metabolites (Chevalier et al., 2000). C. aspersum will preferentially eat plants rich in calcium such as Urtica dioica (Iglesias and Castillejo, 1999; Chevalier et al., 2003) and reject plants rich in metals, such as zinc and nickel (Boyd et al., 2002; Chevalier et al., 2003). Humus ingestion has also been reported as important in the diet of C. aspersum, improving digestibility of food and enhancing growth of juveniles (Perea et al., 2008).

Diet varies over the life cycle: in hatchling snails, oophagy during the hatching period inside the hollow in which the clutch was laid has been reported, significantly enhancing growth and survivorship (Desbuquois and Madec, 1998); after a few days, this behaviour is lost. Juveniles feed more often on fresh plant material than do adults (Iglesias and Castillejo, 1999).

In snail farms, a dry food (powder or pellets) is often used, composed of cereal flour (essentially soya, corn, wheat, sunflower, rye, oats) and enriched in vitamins and calcium. In the laboratory a mix of powdered calcium carbonate, dried milk powder and instant breakfast cereal has been used successfully to rear snails (Cowie and Cain, 1983).

Environmental Requirements

C. aspersum is a generalist species, found in a large range of habitats and climates, from Mediterranean to temperate, oceanic and tropical (Chevallier, 1977).

Activity necessitates a temperature of between 7 and 28°C and an elevated humidity of 75-90% (Daguzan, 1980). If conditions are unfavourable, adult snails are able to remain dormant for several months. However, they cannot withstand long periods of frost (Ansart et al., 2002). Eggs are particularly sensitive to dehydration (Machin, 1975; Riddle, 1983) and cold temperatures (Le Calvé, 1995; Ansart et al., 2007), such that in temperate regions egg deposition occurs only in spring and autumn (Madec and Daguzan, 1993).

Habitats are also highly variable, but the snails preferentially choose microhabitats with greater light intensity and structural complexity, offering more dormancy retreats and better protection against predators, and reject dimly lit microhabitats with smooth substrates (Perea et al., 2007). As the availability of calcium is critical for shell construction, richness in calcium is often suggested as an important criterion for microhabitat selection (e.g. Crowell, 1973).

In culture, crowding rapidly and persistently affects growth of juveniles, with accumulation of slime and faecal matter suggested as having a negative effect on individuals (Cowie and Cain, 1983; Lucarz and Gomot, 1985; Jess and Marks, 1995).

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Natural enemies

Notes on Natural Enemies

To date, no natural enemy specific to C. aspersum is known. Terrestrial snails are a food source for many animals, including mammals (rodents, hedgehogs, shrews, badgers, wild boars, mustelids), many bird species (magpies, thrushes, blackbirds, ducks, owls), reptiles (lizards, turtles, snakes), amphibians (frogs, salamanders, newts), myriapods, insects (some Diptera, Carabidae, Staphylinidae, Lampyridae, Silphidae), planarians, spiders (Porrhothele antipodiana) and predatory terrestrial snails (e.g. Euglandina rosea, Rumina decollata, used for biological control) (for complete information, see Barker, 2004). In certain regions, human predation for consumption purposes can also be important.

Some ectoparasite species have also been described, such as the hematophageous mite Riccardoella limacum, living in the lung cavity of terrestrial gastropods. Flechtmann and Baggio (1985) studied the effects of R. limacum on C. aspersum and reported that when the mite population was sufficiently high, there was high mortality among snails. It has also been shown to influence life history (decreased activity, reproductive output and winter survival) in a related species (Schüpbach and Baur, 2008).

Endoparasitic nematodes (Alloionema appendiculatum, Nemhelix bakeri, Phasmarhabditis hermaphrodita, Rhabditis maupasi, Angiostoma aspersae) can also affect reproduction or cause mortality, particularly in rearing farms (Morand et al., 2004).

Epizootic diseases, regularly appearing during the dry season in C. aspersum rearing farms, have been related to pathogenic strains of the bacterium Aeromonas hydrophila (Kiebre-Toe et al., 2005) and yellow fluorescence leading to death could be caused by pigment-forming bacteria of the genus Pseudomonas (Raut, 2004).

Eggs of C. aspersum can be invaded by microbes, notably fungi. The most frequently described fungus is a Fusarium species, responsible for 'pink clutches', triggering egg degradation (Meynadier et al., 1979).

Means of Movement and Dispersal

Natural Dispersal 

At a local scale, C. aspersum seems to have developed a dispersal strategy involving a fluctuating sexual asymmetry. Fearnley (1993) observed that only a low proportion of large protandrous snails were involved in exchanges between demes in a metapopulation and in the colonization of new areas. This dispersal tendency is promoted by an increase in population density. Such a strategy could explain the successful colonization of agrosystems, which could be considered stressful for snails because of many unpredictable (predation, agricultural practices) and predictable (climate) mortality factors (Madec et al., 2000). However, dispersal has to be set against the cost of locomotion, which is high in snails (Denny, 1980) and C. aspersum has a well-developed homing behaviour (Potts, 1975; Bailey, 1989; Lorvelec, 1990). Thus, active dispersal in C. aspersum allows only slow local diffusion through fragmented landscapes.

Vector Transmission 

C. aspersum, in common with other pulmonate invaders, has been widely distributed throughout the world by human activities. It seems that initial colonization of north-western Europe by the Romans, who initiated snail farming, largely contributed to the massive and rapid dissemination of the species throughout the northern part of its range.

No other species known to be involved in the local dissemination of other species of snails, especially some bird species, seems to be an efficient vector for the passive dispersal of C. aspersum.

Accidental Introduction

Few accidental introductions have been recorded. Although often initially intentionally imported for culture, the snails may then escape from the farming facilities, as has happened in California, Colombia and probably many other places. In Austria, the species may have been introduced accidentally with vegetables. In the Pacific islands, it was intercepted in in Niue and Samoa (in 2002 and 2006, respectively) on containers originating from New Zealand, and in Fiji on wooden pallets (origin not specified). Also intercepted on plant shipments to Florida, it has not become established in this state (PESTNET, 2015).  

Intentional Introduction

C. aspersum has been deliberately introduced to many countries (northeastern Europe, North and South America, Asia, etc.) for economic reasons (source of human food and cosmetics).

Plant Trade

Impact Summary

Impact

In general, there is very little information on the economic damage terrestrial snails and slugs cause to vegetable crops and fruit trees. It has been estimated that Spanish farmers apply 2500 tonnes of molluscicides a year, at a cost of 1000 millions pesetas (£5 million) (Castiellejo et al., 1996). Annual control costs in California, USA, are estimated to exceed US$7 million. In fruit farming, up to 50% of the harvest has been lost as fruit damaged by snails is affected by Monilia fungi (Stringer, 1969; Stringer and Morgan, 1969).

Economic Impact

C. aspersum can cause serious losses to various ornamental plants and crops such as cabbage, lettuce, tomato, citrus, avocado, grapevines and other fruits and vegetables. It can especially be a problem following wet winters and springs.

In the citrus orchards of California, infestation can reach as high as 1000 individuals per tree. In high-rainfall years, fruit losses are often in the order of 40-50% and sometimes reach 90-100% (Sakovich, 2002).

In South African viticultural regions, C. aspersum causes crop losses up to 25%. Moreover, active animals leave mucous trails on the developing grapes, reducing their aesthetic appearance and rendering table grapes unsuitable for export markets (Sanderson and Sirgel, 2002).

In Australia, a significant increase in the level of snail (C. aspersum and Theba pisana) contamination in dried grapes has been observed since the late 1980s, leading to penalties imposed on growers delivering contaminated products. Infestations of 50-70 C. aspersum per vine have been recorded (Sanderson and Sirgel, 2002).

In the USA and New Zealand, C. aspersum creates problems in commercial kiwifruit fields. Fruits with snail damage (up to 35% of kiwifruit harvested) prior to harvest have significantly more Botrytis cinerea grey mould than fruits without damage (Michailides and Elmer, 2000). Moreover, slime trails deposited on fruits stimulate the germination of B. cinerea.

As a consequence, molluscicide usage has increased 70-fold since the early 1970s. In the UK, 4800 tonnes (250 tonnes of active ingredient) were being applied each year at a cost of nearly £10 million, and Spanish farmers were spending £5 million each year on molluscicides (Garthwaite and Thomas, 1996).

Environmental Impact

Impact on Habitats

There are few studies on the impacts of C. aspersum in its natural habitat, as it is essentially a pest in human-disturbed habitats. However, in New Zealand (Barker and Watts, 2002), it is particularly abundant in indigenous ecosystems and potentially constitutes a threat through:

1) selective feeding, which can modify the structure of plant communities;
2) substantial deposit of mucus and faecal material, leading to increasing bacterial and fungal biomass, and hence increased decomposition rates (Theenhaus and Scheu, 1996);
3) introduction of new parasites associated with the snails, such as the mite Riccardoella limacum, which could infect indigenous species;
4) acting as a new food resource for mammalian and avian predators.

It has also been suggested that terrestrial gastropods may influence metal fluxes through soil ecosystems, simply by their preferential selection of certain types of food (Dallinger et al., 2001). In general, terrestrial gastropods are important in nutrient cycling and plant litter decomposition (Meyer et al., 2011, 2013).

Impact on Biodiversity

Little information is available on the impact of C. aspersum on biodiversity. However, when abundant, C. aspersum can monopolise food resources and dormancy retreats that are critical to indigenous mollusc species. Barker and Watts (2002) emphasised the potential impact of C. aspersum on locally endemic species in New Zealand, such as Placostylus ambagiosus and Succinea archeyi.

Social Impact

In certain localities, C. aspersum can be abundant in private and public gardens and destroy ornamental plants and flowers, which can necessitate application of molluscicides.

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad 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
• Tolerant of shade
• Capable of securing and ingesting a wide range of food
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential
• Gregarious
• Has high genetic variability

• Ecosystem change/ habitat alteration
• Host damage
• Infrastructure damage
• Negatively impacts agriculture
• Negatively impacts livelihoods
• Damages animal/plant products

• Interaction with other invasive species

• Highly likely to be transported internationally accidentally
• Highly likely to be transported internationally deliberately
• Highly likely to be transported internationally illegally
• Difficult to identify/detect as a commodity contaminant
• Difficult/costly to control

Uses

Economic Value

C. aspersum is highly prized as an edible snail, primarily in Europe but also in Asia, North America and Africa. In France, although the traditional restaurant ‘escargot’ is Helix pomatia, commercial heliciculture is primarily of C. aspersum (Dupont-Nivet et al., 1997). Heliciculture is also performed in many other countries (e.g. Italy, Greece, Spain, Romania, Poland, North Africa, China, Argentina, Indonesia, USA, Australia) and has been promoted in developing countries where this activity can represent an inexpensive protein source for local consumption as snail meat is high in protein (37-51%). From a conservation perspective, snail farming should be encouraged to prevent overexploitation of wild populations in the native range, and from the perspective of the growing human population, development of such alternatives to traditional agricultural products should be encouraged. Heliciculture, as with other mini-livestock production efforts, represents a new branch of sustainable animal production promoted by the Bureau for Exchange and Distribution of Information on Mini-livestock (BEDIM) in Belgium under the auspices of the European Union and FAO (Hardouin and Thys, 1997).

In French cuisine, snails are called 'escargot' and there are many recipes for cooking them. Less developed is the consumption of the eggs, called 'caviar d’escargot'.

C. aspersum is also raised for pharmacological purposes as the chief ingredient in certain skin creams and gels.

Social Benefit

C. aspersum is important in gastronomy. The typical French 'escargot' (traditionally Helix pomatia but increasingly also C. aspersum) is served in the shell with garlic and parsley butter, but snails are also grilled, stewed or boiled depending on country and tradition. In Catalonia (Spain), a celebration, the 'Aplec del caragol', takes place each May, drawing more than 200,000 visitors, consuming 12,000 tonnes of snails (not only C. aspersum).

Because it is so easy to raise, C. aspersum may also be kept as a household pet. Some internet sites give very comprehensive information on the species and its habits as advice for its maintenance as a pet. For the same reasons, it also represents a frequent 'model' in school classrooms for teaching purposes.

C. aspersum has also gained popularity as an ingredient in skin creams and gels used to reduce wrinkles, scars, dry skin and acne. Several studies have proved the efficacy of C. aspersum extract to repair skin damage, to heal partial thickness burns and to moderate inflammatory responses (Brieva et al., 2008; Tsoutsos et al., 2008).

Environmental Services

C. aspersum can be used as a bioindicator of soil and atmospheric pollution. It is well known for its bio-accumulation of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) and other substances (polycyclic aromatic hydrocarbons) in its soft tissues (digestive gland, mantle tissue) (Gomot de Vaufleury, 2000; Gomot de Vaufleury and Bispo, 2000; Beeby and Richmond, 2002; Viard et al., 2004; Regoli et al., 2006; Sverdrup et al., 2006; Ianistcki et al., 2009). Among valuable biomarker assays tested and currently used for monitoring polluted habitats and assessing the impact of contaminants on the biota, are metallothionein induction, increased biotransformation activity and peroxisomal proliferation (Gomot, 1997; Gomot de Vaufleury and Kerhoas, 2000; Gomot de Vaufleury and Pihan, 2000; Coeurdassier et al., 2002; Dallinger et al., 2004a, b, 2005). Specific cellular changes in response to fungicides extensively used in agriculture have been validated as relevant biomarkers of contaminant exposure and accumulation. A significant decrease in digestive epithelium height and area, and in oocyte numbers in the ovotestis of C. aspersum occurs with increased copper oxychloride accumulation and storage (Snyman et al., 2009).

Detection and Inspection

The following information is from the Canadian Food Inspection Agency Cornu aspersum fact sheet (CFIA, 2014).

Indications of an attack by C. aspersum are ragged holes chewed in leaves, with large veins usually remaining; holes in fruit; and slime trails and excrement on plant material.

Adults and larger juveniles are likely to be visible among the host material or attached to the transporting containers. They may also be hidden in protected locations, sealed into their shells to avoid desiccation. Check the undersides of containers and their rims. Small snails and eggs in soil could be difficult to find. C. aspersum hides in crevices and will overwinter in stony ground.

Inspections are best carried out under wet, warm and dark conditions. Under bright, dry conditions it is necessary to thoroughly search dark, sheltered areas where the humidity is elevated, such as under low-growing plants or debris. The snails may bury themselves in loose soil or other matter, so the only way to be reasonably sure an area is not infested is to make repeated surveys over a long period of time.

Similarities to Other Species/Conditions

In North Africa, native populations of C. aspersum exhibit conspicuous shell variation that led to the description of many subspecies or varieties on the basis of shell shape and colour (e.g. Germain, 1908; Taylor, 1914; Chevallier, 1977). However, distinguishing discrete forms is difficult because of the high number of loci involved in the colour variation (Albuquerque de Matos, 1984) as well as in shell size and shape. Three main forms, namely aspersa, maxima and conoidea, are easily recognized and frequently encountered in the Maghreb. The giant form maxima (D > 40 mm) can be distinguished by its pigmentation (dark colour of the mantle edge) and by a very large shell aperture (megalostoma). The form conoidea is characterized by a ratio of width to height > 1. Only the form aspersa (the common garden snail) is widespread around the world, in regions with Mediterranean, temperate and even subtropical climates. The forms aspersa and maxima are the two forms that are commonly reared.

Confusion with other species is highly improbable. In the escargotières of the Maghreb a common mistake is to misidentify Helix melanostoma as C. aspersum, but live specimens of H. melanostoma have a thicker and paler shell that has a dark peristome without a reflected lip.

In other countries, i.e. in northwest Europe and other more recently colonized regions, there is no risk of confusion.

Prevention and Control

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

The Canadian Food Inspection Agency (CFIA, 2014) considers C. aspersum to be a plant pest and have quarantines established for preventing the importation of the snail in plant and soil matter. The United States Department of Agriculture requires a permit to import snails (or slugs) into the USA and between states within the USA from APHIS, Animal Plant Health and Inspection Service (APHIS, 2002).

Public Awareness

APHIS (2009) encourages people using C. aspersum in classrooms, nature facilities, or keeping them as pets to turn them in voluntarily. Some US states have created an ‘invasive species hotline' (e.g. Oregon, Hawaii, Michigan) for early detection of potential pest invaders. Residents of the state of Hawaii are asked to be on the lookout for this pest and to call a resident agricultural specialist on their respective island if they see this snail. It is currently recorded on only two of the Hawaiian Islands (Cowie, 1997; Cowie et al., 2008)

Containment/Zoning

In the USA, APHIS has produced containment guidelines to assist a researcher, educator, or commercial entity to design, build, maintain and operate a facility for rearing nonindigenous snails in the USA, including C. aspersum (APHIS, 2002), the non-respect of which is subject to civil and/or criminal penalties and loss of permits.

Control

Physical/Mechanical and Cultural Control

Handpicking with subsequent destruction of animals is the oldest method of control of pest molluscs. Even though it is time intensive, it can be effective as C. aspersum is gregarious and can be found in huge numbers under snail traps. Other places around susceptible plants where snails can hide during daily or seasonal dormancy, such as boards, debris and dense cover such as ivy, branches growing near the ground, stones, must be removed (Barker and Watts, 2002; Dreistadt et al., 2004).

Physical barriers such as continuous lines of wood ash, sand or diatomaceous earth can be effective for short-term control but their effectiveness is drastically reduced once they become wet (Davis et al., 2004; Dreistadt et al., 2004). Lines of lime and copper sulphate or copper screen are repellent to snails and can be used to prevent movement into an area. Various other organic and inorganic substances have been used as barriers to prevent snails getting access to plants. These barriers have proved to be moderately successful, and their effectiveness is greatly improved as part of an IPM approach along with pit-fall traps and hand collecting.

Containers filled with beer attract slugs and snails, but beer must be replaced regularly to be effective.

Bordeaux mixture (a copper sulphate and hydrated lime mixture) can be brushed on tree trunks to repel snails, one treatment should last about a year (Dreistadt et al., 2004). Thin copper sheets can also be wrapped around tree trunks to prevent snails from climbing into the canopy (Davis et al., 2004; Dreistadt et al., 2004). Du Toit and Brink (1993) tested treatments for the control of C. aspersum in citrus trees in South Africa, including chemical control using copper sulphate, metaldehyde and copper oxychloride, but the only treatment that reduced snails to an average of less than two per tree after 29 weeks was a copper strip around the stem preventing snails from climbing up it. The strips were 0.127 mm thick and 50 mm wide, and were fastened 500 mm from the ground with a paper-clip. They were still effective 12 months after application, and are recommended as a long-term control method. Removal of the lower branches of trees by pruning can minimize the contact of the foliage with the ground and help to reduce the number of C. aspersum on the trees. In California, skirt-pruning associated with copper sheets on the trunk and handpicking of snails stopped by this barrier can be very effective (Sakovich, 2002); and although no longer practised, running cultivation equipment through an orchard several times a year contributed to control of C. aspersum through destruction of buried egg clutches and snails buried in the ground (Sakovich, 2002).

Biological Control

As terrestrial molluscs have many natural enemies, there has been strong interest in the biological control of C. aspersum using other, predatory snails (e.g. Fisher and Orth, 1985). However, as most of these predatory snails are not host-specific, they are not appropriate to use in control programmes in which effects on non-target species are of concern (Cowie, 2001: Barker and Watts, 2002).

There have been several attempts to develop biological control of C. aspersum in California, South Africa and New Zealand, which began with the introduction of predaceous snails (Euglandina rosea, Gonaxis sp.) and beetles during the 1950s and early 1960s (for more information see Fisher and Orth, 1985; Barker and Efford, 2004). These efforts were largely unsuccessful, although one staphylinid beetle (Staphylinus (Ocypus) olens) showed potential; however, the use of this species as a biological control in orchards has not been actively pursued (Sakovich, 2002). In 1966, however, another (opportunistic) predaceous snail, the decollate snail Rumina decollata (of European origin) was found to have invaded California (see Pictures). Experimental releases of R. decollata in southern California citrus orchards were begun in 1975 and, in most cases, resulted in complete control (displacement) of C. aspersum (Fisher and Orth, 1985). Rumina decollata is now used to control C. aspersum in some 20,000 ha of citrus in southern California, but is currently permitted only in certain Californian counties (Dreistadt et al., 2004). As this predatory snail consumes young to half-grown snails, control is achieved only in 4-6 years. Sakovich (2002) recommended first using molluscicidal baits to reduce the population, and then combining skirt-pruning and copper barriers with introduction of R. decollata. Once control by R. decollata is achieved, maintenance of copper barriers can cease, R. decollata can be harvested and transferred to new areas. However, Cowie (2001) expressed concern regarding both the effectiveness of R. decollata in control of C. aspersum, its potential impacts on native (even endangered) species and its potential as a garden plant pest.

A study by Altieri et al. (1982) was carried out in a daisy field in northern California to determine the effectiveness of the indigenous coleopterous predator Scaphinotus striatopunctatus in the biological control of C. aspersum. Release of the predator in the field under light metal sheets, together with colonization by garter snakes (Thamnophis elegans) from an adjacent field, resulted in a significant reduction in snail populations.

In South Africa, the native predacious gastropod Natalina cafra was investigated as a potential biological control agent against C. aspersum, with special attention to the possibility of establishing a viable population of the natural enemy in captivity (Joubert, 1993), but this approach seems not to have been implemented.

Research by the Entomology Division of the Plant Protection Department, Cukurova University, Turkey, on the importation of predators and parasitoids as biological control agents (mainly for citrus pests) included the coccinellid Hippodamia convergens as a potential predator of C. aspersum (Uygun and Sekeroglu, 1987).

Ducks, chickens or guinea fowl can provide long-term control in citrus orchards and vineyards, if an appropriate breed is chosen and properly cared for. Growers take the animals each morning into the orchard for as little as half an hour to scavenge for food. This solution can be very effective but involves extra labour in managing the animals and protecting them from predators (Sakovich, 2002; Davis et al., 2004).

Chemical Control

Application of molluscicides is the most widely implemented approach to controlling snail pests. However, they do not totally control snails and must be used properly and in conjunction with other methods (physical, biological) in integrated management (Flint, 2003). Molluscicides are generally delivered as baits (e.g. de Boodt et al., 1990), and also exist as sprays and dusts but have proved less effective under these formulations. There are three major classes of compounds present in molluscicides: metaldehyde (induces desiccation and loss of locomotor activity), carbamates (causes paralysis and loss of muscle tone), and metal chelates such as iron EDTA (interacts with oxygen uptake and triggers arrest of feeding) (Barker and Watts, 2002).

However, baits are toxic to the decollate snail and to other non-pest gastropods, and certain materials may poison pets (Dreistadt et al., 2004).

To be effective, baits must be sprinkled preferentially when the snails are active (Flint, 2003). The formulation and dose to apply will depend on environmental conditions (for more information, see Barker and Watts, 2002).

Laboratory and field experiments have been conducted in Egypt to investigate the molluscicidal activity of weed extracts from Ambrosia martine, Citrullus colocynthis, Cymbopogon proximus and Glinus sp., and of five fertilizers, against C. aspersum. Ambrosia martine extract was shown to be the most toxic, followed by C. colocynthis and C. proximus, while Glinus sp. was the least effective. Snail mortality increased gradually with time. Some commonly used fertilizers showed considerable initial and residual molluscicidal effects. Ferrous sulfate was the most effective against C. aspersum, followed by ammonium nitrate, ammonium sulfate and superphosphate (Zidan et al., 1997).

A patented copper complex, formulated as a spray and referred to as copper silicate, shows molluscicidal activity (Davis et al., 1996). The product was tested in both spray and granular formulations against C. aspersum in a vineyard and a citrus orchard in Western Australia, where it was compared with copper oxychloride spray. The copper complex spray demonstrated a high level of repellence to C. aspersum for extended periods in the field, and proved superior to the other products tested in reducing snail numbers in vines/trees. The product has potential in the management of pest molluscs, especially as part of IPM programmes, but it seems not to have been further developed.

Control by Utilization

In some places gathering snails free for personal consumption is permitted, e.g. from artichoke, kiwifruit, avocado and citrus growers, although it is recommended to purge them at least 3 days to remove traces of poison baits that might have been ingested.

Gaps in Knowledge/Research Needs

Much work on C. aspersum has been conducted on aspects of its life history under artificial conditions because of the economic value of heliciculture. Some fundamental points of its biology have also been studied from an evolutionary point of view. However, only a few studies deal with the ecology of natural populations (demography, dispersal, interspecific interactions), and no-one has studied phenotypic evolution in response to global change, i.e. adaptive responses to the variation in landscape structure and environmental pressures. Studies on resistance to molluscicides (present formulations do not seem to be very effective against C. aspersum) and to pesticides more generally, would be valuable because these substances have direct toxic effects that may result in enhanced mortality and/or adaptive responses.

Thus, a research programme based on theoretical and empirical studies that would lead to generalizations on (i) the genetic architecture of the combinations of life-history characteristics involved in invasions, (ii) responses to selection and (iii) the model of spread of populations in recently invaded areas is clearly needed. Such a programme is predicated on invaded areas being identified beforehand.

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Links to Websites

Contributors

07/08/15 Updated by:

Robert Cowie, Pacific Biosciences Research Centre, University of Hawaii, Honolulu, Hawaii, USA

24/07/09 Original text (for ISC) by:

Armelle Ansart, Université de Rennes 1, 263 Av. du Gal Leclerc, CS 74205, 35042 Rennes Cedex, France

Luc Madec, Université de Rennes UMR CNRS 6553 ECOBIO, Campus de Beaulieu, Bât. 14A Av du Général Leclerc, F-35042 Rennes Cedex, France

Annie Guiller, Laboratoire de Parasitologie, UMR CNRS 6553, Université de Rennes, Av. du Pr. Léon Bernard, 35043 Rennes, France

Distribution Maps