Deroceras laeve
(meadow slug)

Pictures

Picture	Title	Caption	Copyright
Title Adult Caption Deroceras laeve (meadow slug); from marshland. County Down, Northern Ireland, UK. Copyright ©Roy Anderson	Adult	Deroceras laeve (meadow slug); from marshland. County Down, Northern Ireland, UK.	©Roy Anderson
Title Adult Caption Deroceras laeve (meadow slug); from alder carr. County Antrim, Northern Ireland, UK. Copyright ©Roy Anderson	Adult	Deroceras laeve (meadow slug); from alder carr. County Antrim, Northern Ireland, UK.	©Roy Anderson
Title Adult Caption Deroceras laeve (meadow slug); greenhouse form. Belfast, Northern Ireland, UK. Copyright ©Roy Anderson	Adult	Deroceras laeve (meadow slug); greenhouse form. Belfast, Northern Ireland, UK.	©Roy Anderson
Title Adult Caption Deroceras laeve (meadow slug); from woodland. County Dublin, Republic of Ireland. Copyright ©Roy Anderson	Adult	Deroceras laeve (meadow slug); from woodland. County Dublin, Republic of Ireland.	©Roy Anderson

Identity

Preferred Scientific Name

• Deroceras laeve Müller

Preferred Common Name

• meadow slug

Other Scientific Names

• Agriolimax agrestis L.
• Agriolimax berendti var. pictus Cockerell
• Agriolimax bovenoti Collinge
• Agriolimax campestris zonatipes Cockerell
• Agriolimax globosus Collinge
• Agriolimax pellucidus Chen & Gao
• Agriolimax perkinsi Collinge
• Agriolimax pseudodioicus Velitchkovsky
• Agriolimax renschi Wagner
• Deroceras schulzi Y. Tzvetkov & Matyokin
• Krynickillus minutus Kaleniczenko
• Limax agrestis L.
• Limax araneus Gessis
• Limax berendti var. pictus Cockerell
• Limax brunnaeus Draparnaud
• Limax brunneus Draparnaud
• Limax campestris A. Binney
• Limax castaneus Ingersoll
• Limax fedtschenkoni Koch & Heynemann
• Limax gracilis Rafinesque
• Limax hemphili W.G. Binney
• Limax heydeni Heynemann
• Limax hyperboreus Westerleund
• Limax ingersolli A. Binney
• Limax laevis Muller
• Limax montanus Ingersoll
• Limax nicensis Bourguignat
• Limax norvegicus Westerlund
• Limax pallidus Schrenk
• Limax parvulus Normand
• Limax veranyanus Bourguignat
• Limax weinlandi Heynemann

International Common Names

• English: brown slug; marsh slug; smooth slug
• Spanish: babosa; babosa gris chica
• French: limace champêtre

Local Common Names

• Brazil: lesma
• Germany: Wasser-Egelschnecke

Summary of Invasiveness

D. laeve is native to the Palaearctic and to at least the western half of the Nearctic. This species is frequently confused with other species in the genus Deroceras, in particular D. invadens. As a result the exact distribution of this species is uncertain. There is reliable evidence for its invasiveness in many other parts of the world. It is widespread in mountainous regions of South America where it is unlikely to be native (Hausdorf, 2002), although has been present for a long time, at least since the late nineteenth century (Simroth, 1910). It is also present in the Pacific islands, Australia and New Zealand. This species has a number of important survival strategies such as significant freeze tolerance and a well-developed anaerobic metabolism which allows it to stay underwater for days. In Hawaii it is believed to have a negative impact on a critically endangered species, Alsinidendron obovatum.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Mollusca
•             Class: Gastropoda
•                 Subclass: Pulmonata
•                     Order: Stylommatophora
•                         Suborder: Sigmurethra
•                             Unknown: Limacoidea
•                                 Family: Limacidae
•                                     Genus: Deroceras
•                                         Species: Deroceras laeve

Notes on Taxonomy and Nomenclature

Deroceras is a large genus of terrestrial pulmonate slugs with at least 123 species (Wiktor, 2000). D. laeve is the most widespread taxon and has a large number of synonyms with 20 specific names listed by Kennard and Woodward (1926) and 21 by Wiktor (2000). This is mainly reflective of the variability of the species in body size, colouration and degree of development of the male copulatory organs and of its very wide distribution.

In North America this inherent variability has led to the recognition of allied but separate species by Pilsbry (1948). D. monentolophus Pilsbry has subsequently been synonymised with D. laeve by Wiktor (2000) who also expressed doubt about the specific distinctness of D. hesperium Pilsbry. Recently acquired molecular data on D. hesperium has led to the conclusion that this is not a separate species either and should now be reduced to synonymy with D. laeve (Roth et al., 2013).

Rowson et al. (2014b) when examining British Deroceras at the molecular level concluded that the greenhouse form of D. laeve is specifically distinct. This is important as the greenhouse form is readily transported with horticultural materials and is probably widely spread in artificial environments across the world. They also posited a genetically distinct form of laeve from wetlands in Ireland but this hypothesis needs to be more widely tested.

Essentially, the nomenclature of this species is well documented (Kennard and Woodward, 1926; Wiktor, 2000) and the taxonomy is clear. Confusion, however, has arisen in the conflation of D. laeve with other invasive Deroceras species and particularly with D. invadens (Reise et al., 2011; Hutchinson et al., 2014). D. invadens is genetically and physically distinct from D.laeve but many workers in South America, Australia and the USA have in the past, failed to distinguish it from D. laeve (Hutchinson et al., 2014). This has probably distorted our understanding of the distribution, behaviour and agronomy of the species as reported in the literature and should be borne in mind when viewing this datasheet.

Description

D. laeve is a small slug usually less than 22 mm long and sometimes much less. However, specimens from North America may be larger than 25 mm and overlap in size with the generally larger D. invadens. The body is cylindrical and somewhat broader distally. The mantle is unusually large in proportion and has delicate wrinkles visible in front, in live specimens. The tail section of the body is shorter than the mantle section. The back either slopes evenly towards the tail or is squared off and moderately truncate. A small keel is present close to the tail (Rowson et al., 2014a). 

It is variable in ground colour, ranging from an opaque chestnut- through grayish-brown to chocolate-brown. On close examination the back is seen to be sparsely mottled a darker shade, which is not easily visible to the naked eye. The mantle is similarly, or perhaps more densely, spotted. The sole is the same shade as the upper surface and the respiratory pore is only slightly paler than the rest of the body but individuals with more conspicuously pale-rimmed pores are reported from North America. Pedal and body mucus is colourless.

D. laeve is peculiar in having a partial or entire reduction of the male copulatory organs in most specimens (aphallic condition). Specimens with a fully developed penis (euphallic) are rare or absent in many populations but where euphally occurs the penis is elongate and spirally twisted (Rowson et al., 2014a). The distal intestine lacks a caecum (Wiktor, 2000).

Eggs - 1.8 x 1.5 to 2 x 1.3 mm; translucent, with calcareous particles (Quick, 1960).

Distribution

The original native range of D. laeve is considered to be the Palaearctic and parts of the Nearctic (Wiktor, 2000). This species was accidentally introduced into new areas where it reached mountainous regions of the Neotropics quite early (nineteenth century). It later became established in non-mountainous parts of some South American countries, Australia, New Zealand and a range of Pacific Islands.

This species effectively now occurs on all continents except the Antarctic. Confusion with other species such as D. invadens, partly obscures understanding of its distribution outside the native range.

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

Very little is known about means, rate of travel and date of transfer of D. laeve into new territories. The greenhouse form of D. laeve recognised in Britain and Ireland (Rowson et al., 2014a; Rowson et al., 2014b) may have been accidentally introduced into new areas with horticultural produce. The transfer of D. laeve with agricultural materials of both forms is also possible but undocumented.

In 1897, D. laeve was first recorded in Hawaii (Cowie, 1997). Today it is believed that it is likely to be present on all of the main islands such as Lanai, Kauai, Oahu and Maui.

In South America, D. laeve was is believed to have been introduced by the agricultural trade and was recorded in Colombia before 1910, Uruguay in 1963, Chile in 1985 and Veneuzela before 1970 (de Fernandez, 1982; Cowie, 1997; Campos and Calov, 2006l; Araya, 2015).

In 2001, D. laeve was found in Duikar village, Gilgit District, northern Pakistan. This new record, the highest located in Karakoram, is believed to be an extension of its continuous distribution in the mid-Hunza river region (Hlavac, 2004).

Introductions

Risk of Introduction

Due to the fact that D. laeve is present on all continents, except Antarctica, it is likely that the risk of this species being introduced into new areas is high. This is likely to occur accidentally with plants, good or waste including agricultural or garden waste (Thomas et al., 2010).

Habitat

D. laeve is partially amphibious and is present across a large range of habitats. These include moist habitats such as wet marshes, wet woodlands, fields, river banks and meadows and it can sometimes be found in greenhouses and as a garden pest (White-McLean and Redford, 2011). It is typically found from sea level to altitudes of greater than 4,800 m. In its native range, D. laeve takes refuge under leaf litter and woody debris (Thomas et al., 2010).

Habitat List

Hosts/Species Affected

A wide range of plants are consumed by D. laeve including Fittonia, Datura stramonium and species of Lilium, Iris, Narcissus, Chrysanthemum, Fragaria and Cyclamen (Getz, 1959). In China D. laeve has been observed to feed on broad beans (Vicia faba) and species of Brassica in rural villages (Wiktor et al., 2000), in Canada on strawberries (Fragaria × ananassa) in farms (Prystupa et al., 1987) and in the USA on weeds and some crops in no-tillage cropping systems (Rogers et al., 1985). Its wild food has not been studied fully but probably includes both live and dead green plants in the habitats it frequents (Wiktor, 2000).

Host Plants and Other Plants Affected

Growth Stages

List of Symptoms/Signs

Biology and Ecology

Reproductive Biology

D. laeve is an annual species and can grow rapidly to maturity in as little as a month (AnimalBase, 2015). It can potentially reproduce all year round (Jordaens et al., 2006). Although outcrossing has been recorded, many populations are aphallic and reproduce uniparentally. Eggs are laid singly or in small clusters, mainly in spring but probably at any time of year. They are large relative to the slug’s body size, at 2 x 1.5 mm and are translucent and finely punctuate, lacking a calcified shell (Quick, 1961).

Physiology and Phenology

This species lives in areas where it may be submerged frequently. As a result, it appears to be able to switch to anaerobiosis under water (Storey et al., 2007) and can survive immersion for days, as can its eggs. Juveniles can hatch under water and will migrate to the surface. As might be expected of a species which can live within the Arctic Circle, it has a wide temperature tolerance (0-30^oC) and can survive freezing (Getz, 1959). A 100 fold increase in glucose levels have been recorded which are believed to provide a cryoprotective function during freezing (Storey et al., 2007).

D. laeve is a small, fast-moving and agile slug though not as irritable as D. invadens. Strikingly, it can continue to move flexibly under water and its pedal mucus does not seem to be easily washed off by immersion.

Longevity

Maximum life span is about one year but it can progress from egg to maturity in about one month.

Activity Patterns

D. laeve can reproduce at almost any time of year in the temperate zone and probably in other regions of the world (Rowson et al., 2014a).

Nutrition

D. laeve will feed on plant material and also carrion and live invertebrates (Herbert, 2010). Under laboratory conditions D. laeve may eat up to 40% of its total body weight per day (Osborne, 2015).

Environmental Requirements

Deroceras laeve has a wide temperature tolerance and can survive five hours at -8°C, although not at -10°C (Getz, 1959). It is very hygrophilous and usually found in the vicinity of water where other slugs tend not to occur but can enter damp woodlands and farmland under suitable conditions (Rowson et al., 2014a).

Climate

Latitude/Altitude Ranges

Air Temperature

Natural enemies

Notes on Natural Enemies

Predators of D. laeve include a number of ground beetle species of the genera Carabus and Cychrus (for example Cychrus caraboides), silphid beetles such the European species Silpha atrata, and mammalian (Eurasian hedgehog, Erinaceus europaeus) and aquatic bird predators (Anas platyrhynchos). In addition, species of Sciomyzidae (marsh or snail-killing flies) may be important in controlling numbers in natural habitats of the Palaearctic and Nearctic. Larval sciomyzids actively predate, or more often, parasitise gastropods in aquatic or semi-aquatic habitats. For instance, Tetanocera plebeia and T. valida are host specific as newly hatched larvae, for D. laeve and D. reticulatum (Trelka and Foote, 1970). In Europe T. elata is a potential biocontrol agent for D. reticulatum (Hynes et al., 2014) but also parasitises D. laeve.

Means of Movement and Dispersal

Natural Dispersal

D. laeve can be naturally dispersed over short distances by water and flooding events (AnimalBase, 2015).

Vector Transmission

Passive migration on birds or mammals has not been recorded but is certainly possible, as with all invertebrates sharing aquatic habitats with migratory birds.

Accidental Introduction

D. laeve may be accidentally introduced into new areas as a contaminant linked with the transport of food, consumed goods, or in garden waste.

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

D. laeve can be a serious pest of greenhouses (Animalbase, 2015), feeding on both living and dead plant material (Wiktor, 2000). This species may also impact some no-tillage agricultural systems in the USA (Rogers et al., 1985). Estimates of economic losses due to this species have not been calculated.

Environmental Impact

Impact on Biodiversity

D. laeve sensu stricto is largely confined to habitats not occupied by many other slugs and rarely achieves population densities sufficient to impact natural plant communities. It may, however, have an impact on threatened plant species in vulnerable ecosystems (Joe and Daehler, 2008). There is some evidence indicating that D. laeve is impacting on the critically endangered Alsinidendron obovatum in Hawaii and also on Cyanea superba (Joe and Daehler, 2008).

Threatened Species

Social Impact

D. laeve is known as a host for a number of nematodes. These include Angiostrongylus costaricensis, which may infect humans if inadvertently ingested with vegetable crops in areas such as Brazil (Maurer et al., 2002), A. vasorum, a cardiopulmonary parasite in dogs and usually fatal (Nabais, 2012) and A. cantonensis, which has been reported to cause of eosinophilic meningoencephalitis in south-east Asia and the Pacific Islands (Wallace and Rosen, 1969).

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Tolerant of shade
• Capable of securing and ingesting a wide range of food
• Fast growing
• Has high reproductive potential
• Reproduces asexually
• Has high genetic variability

• Changed gene pool/ selective loss of genotypes
• Negatively impacts agriculture
• Negatively impacts human health
• Negatively impacts animal health
• Negatively impacts livelihoods
• Threat to/ loss of native species

• Competition - monopolizing resources
• Pest and disease transmission
• Herbivory/grazing/browsing
• Interaction with other invasive species

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect in the field
• Difficult/costly to control

Uses

D. laeve can be used in the laboratory as a research model.

Uses List

General

• Laboratory use
• Research model

Similarities to Other Species/Conditions

Other species with which D. laeve has undoubtedly been confused in the past include D. invadens and perhaps D. panormitanum sensu stricto, but to a much less degree (Reise et al., 2011). It is generally assumed that the best distinguishing features from these species is their larger size (25-35 mm) and consistently white-rimmed respiratory orifice. However, in North America D. laeve is known to grow larger than in Europe (also true of other warm countries) and specimens with white-rimmed respiratory orifices are not unknown (Hutchinson et al., 2014). The only safe way of distinguishing the native D.laeve in the USA (and elsewhere) is by dissection.

Little is known of a genetically distinct "greenhouse" form of D. laeve which, while larger and possibly differing in colour from the nominotypical form (Rowson et al., 2014b), has not yet been reliably identified outside Britain and Ireland.

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.

Control

Biological Control

Phasmarhabditis hermaphrodita is a nematode parasite of slugs which, though most effective in controlling D. reticulatum can also kill other species of Deroceras (Speiser et al., 2001). However, this form of control is uneconomic for field crops at present.

Chemical Control

Formulations of copper, metaldehyde and methiocarb were assessed for their efficacy in controlling D. laeve. Prystuppa et al. (1987) found that 2% methiocarb was the most effective treatment with copper failing to provide significant mortalities. It has been suggested that when applied at high concentrations, metaldehyde may act as a repellant to D. laeve and it has been suggested the efficacy of carbamates would be increased if slugs can get to water after treatment (Osborne, 2015).

Gaps in Knowledge/Research Needs

Although D. laeve has been introduced into nearly all regions in the world, there is no clear information on the pathways of dispersal. Studies in this area would be relevant to interrupt transit and prevent new introductions. In addition to this, further studies are required to determine population numbers of this species in its native range as it is believed that they are declining as a result of construction and subsequent habitat destruction (AnimalBase, 2015).

References

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Nabais JNP, 2012. Aelurostrongylus abstrusus and Angiostrongylus vasorum (nematoda: angiostrongylidae) infection in cats and dogs in the district of Lisbon, Portugal. (Infecção por Aelurostrongylus abstrusus e Angiostrongylus vasorum (Nematoda: Angiostrongylidae), em gatos e cães no distrito de Lisboa, Portugal.) Dissertação de Mestrado Integrado em Medicina Veterinária. Lisbon, Portugal: Universidade Técnica de Lisboa, 80 pp.

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Distribution References

AnimalBase, 2015. AnimalBase., Göttingen, Germany: University of Göttingen. http://www.animalbase.org/

Araya J F, 2015. Current status of the non-indigenous molluscs in Chile, with the first record of Otala punctata (Müller, 1774) (Gastropoda: Helicidae) in the country and new records for Cornu aspersum (Müller, 1774) and Deroceras laeve (Müller, 1774). Journal of Natural History. 49 (29/30), 1731-1761. http://www.tandfonline.com/loi/tnah20

Backhuys W, 1975. Land and freshwater molluscs of the Azores. Amsterdam, Netherlands: Backhuys and Meesters.

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Contributors

23/11/15 Original text by:

Roy Anderson, Consultant, Northern Ireland

Distribution Maps