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Deroceras laeve (Müller, 1774)
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Species name:
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Deroceras laeve (Müller, 1774)
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Taxon name:
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Limax lævis Müller, 1774
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Originally described in:
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Müller, O. F. 1774. Vermivm terrestrium et fluviatilium, seu animalium infusoriorum, helminthicorum, et testaceorum, non marinorum, succincta historia. Volumen alterum. - pp. I-XXXVI [= 1-36], 1-214, [1-10]. Havniæ & Lipsiæ. (Heineck & Faber).
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Distribution:
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Originally Palearctic from subpolar zones to the southern margins, today introduced worldwide except Antarctica, also on tropical islands such as New Guinea or on Pacific islands
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Diagnosis:
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Slug brown to dark brown, usually with dark and characteristic but not well visible spots arranged in groups, shape almost cylindrical, posterior end abruptly widened, mantle 50 % of body length (unusually large), wrinkles on skin present (may disappear in preserved slugs). Mucus thin, colourless.
Penis often reduced, elongated if present, without proper penial gland but with two or more tiny glandular papillae and its end, retractor unforked and attached at half penis length, stimulator small, cone-shaped but looks more like a papilla. Tubular oviductus and atrium are unusually long. No rectal caecum.
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Size:
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15-25 mm long (preserved)
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Biology:
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High ecological tolerance, but needs permanently wet habitats. Usually in lowlands and very humid habitats, swamps, riversides, wetlands, especially alder and oak woods, marshlands and degraded areas, also greenhouses, often near water under wood or detritus. Tolerates subpolar and tropical temperatures. Newly created habitats are often colonized after a few years. In Switzerland in up to 1800 m altitude, but usually below 1000 m, in Bulgaria in up to 2500 m.
The only land snail that goes deliberately into the water and can survive for days submerged. Can be dispersed by water currents. Eggs also survive submerged, juveniles can hatch under water and then get to the surface. Slugs are agile, crawl quickly, they are omnivorous, life and dead plant remains are preferred.
3 days after copulation eggs (1-2.5 mm) are laid singly or in small clusters at intervals of some days, in total 20-30 eggs, 3 mm long reddish juveniles hatch after 20-30 days, maturity is reached after 60-80 days, animals die shortly after the egg laying period, usually at 3-5 months age. Maximum age slightly more than 1 year, but only very few animals reach this age. Life cycle in some regions extremely short, down to less than a month, up to 5 generations in a year, several generations can live at the same time. Frequently there are forms with reduced penis, which reproduce by self-fertilisation.
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Threatened:
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Deroceras laeve can be a serious pest in greenhouses. On the other hand the species is threatened by continuous destructions of wet habitats by drainage, construction projects and road construction. The species has shown little evidence for significant decline in Britain.
Lower concern in Switzerland.
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Family:
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Agriolimacidae
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Higher group:
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Gastropoda
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Comments:
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References: Frömming 1954: 206, Kerney et al. 1983: 191, Wiktor 1983, Falkner 1990: 192, Manganelli et al. 1995: 22, Turner et al. 1998: 303, Kerney 1999: 161, Wiktor 2000: 462, Wiktor 2001: 109 (in Greece only one record, from Kea), Pesqueira et al. 2003, Irikov & Mollov 2006: 809, Beckmann 2007: 88 (Mallorca), Hubenov 2007, Welter-Schultes 2012: 464 (range map Europe).
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