Deroceras (Deroceras) reticulatum (Müller, 1774)
Gray fieldslug (English), gray garden slug, reticulate slug, milky slug
The commonest slug in NW Europe (Kerney & Cameron 1979) and the major pest slug in agriculture, worldwide.
In North and central European lowlands, Great Britain and Ireland; probably the most widely distributed slug. Scarce and mainly as a synanthrope in N Scandinavia.
Not aggressive (Rollo & Wellington 1979); aggregations occur with bad moisture and temp levels (Rollo & Wellington 1981). Homes to shelter (Cook 1979).
External: Slug very variable, creamy or light coffee cream, rarely blackish spotted (slugs with spots may appear blackish); behind the mantle the dark spots form a reticulate pattern in the skin grooves; skin thick with large tubercles; pneumostome 2/3 back from front of mantle; pale pneumostome edge; short keel; abrupt truncation of tail tip; 3-part, pale sole; mucus colourless, on irritation milky white (calcareous granules in white mucus).
Internal: Brown ovotestis; albumen gland light brown and liver-shaped; penis fleshy and with a silky sheen, in the shape of an irregular sac, in fully mature specimens divided into 2 parts by a deep lateral constriction; penial gland of very variable shape, usually consisting of a few branches or a single long branch (1-4 knobby processes); stimulator large, conical and narrow; retractor muscle inserted laterally on penis; vas deferens opens into penis wall facing the external body side; short, straight oviduct; narrow spermatheca; small atrium; rectal caecum large.
The slug cannot be distinguished from many other Deroceras species based only on its external appearance. Similar to D. agreste and D. rodnae (Kerney & Cameron 1979); different from D. laeve and D. carunae: opaque skin, white mucus when irritated, bigger size, rectal caecum presence (Quick 1960).
Eggs: 3 x 2.5 mm, translucent, begin with calcareous speckles on surface. Up to 700 eggs are produced per individual slug (Quick 1960).
Juveniles: 4 mm long, light gray and translucent at hatching (Quick 1960).
Deroceras reticulatum is partly freeze-tolerant (experiences mortality at or below -4.7 C for 30+ min.) (Cook 2004).
Up to 40-60 mm long (preserved 25-30 mm); varies in size according to the habitat.
Ecology and Distribution
Native to: Europe, Mediterranean countries, and Atlantic Ids (Quick 1960). More rare and resticted to cultivated fields in the southeast, particularly in the Balkans, probably absent from Greece and Bulgarian mountains.
Introduced as a synanthrope to many regions: North America, Peru, South Africa, Tasmania, New Zealand, central Asia.
Type Locality: Frideriksdal near København, Denmark.
D. reticulatum are attacked by parasites including Sciomyzid glies and nematodes. Some English populations of D. reticulatum have high rates of Sciomyzid fly infection (Stevenson & Knutson 1966, in Hunter 1978). D. reticulatum are susceptible to and experienced mortality from P. hermaphrodita (Grewal et al. 2003), which enter slugs' mantle cavities, reach adulthood, and reproduce (causing swelling of the mantle); the second generation tends to kill slug (Wilson & Grewal 2006).
In defense against predators, Deroceras reticulatum is capable of tail autotomization, followed by fleeing and hiding (Solem 1974; Pakarinen 1994a).
At present almost exclusively restricted to cultivated areas, usually in open habitats, in meadows, near roadsides, in ruins, gardens and parks, not inside forests. Shelters under stones, fallen logs, vegetation, and ground litter (does not burrow into the soil). Can reach high abundances in cultivated land; widespread and common in invaded habitats (Chichester & Getz 1969).
Life cycle covers a few months, usually two generations; main reproductive phase in summer and autumn, maximum age about a year; slugs die at the first frosts. Usually only eggs hibernate, sometimes also juveniles.
In Britain, slugs mate year round; they can reach adulthood in 3 months during summer (Quick 1960). In Michigan, only (a few) adults emerged in early spring, immediately laid eggs after emergence and through the fall, and juveniles appeared in June; here, it is an annual species (Getz 1959).
Species is omnivorous, feeding mainly on fresh leaves and fruits or seedings. Consumes live plants (favored more than most other gastropods), dead plants, and wood (Chichester & Getz 1973; Jennings & Barkham 1975; Herbert 2010).
Deroceras reticulatum is the major slug pest worldwide in agriculture (Ester & Wilson 2006), consuming seedlings and green vegetation (Quick 1960). They are known pests on oilseed rape, cabbage, brussels sprouts, ice berg lettuce, and other plants (Ester & Wilson 2006). After several years with continuous moist weather conditions, abundance can seriously increase.
- Limax reticulatus Müller, 1774 (synonym)
- Limax canariensis d'Orbigny, 1839 (synonym)
- Agriolimax pallidus Schrenk, 1848 (synonym)
- ?Agriolimax Drymonius Bourguignat (synonym)
- Agriolimax simrothi Cockerell, 1893 (synonym)
- ?Limax (Krynickillus) nicensis Bourguignat (in Nevill), 1880 (synonym)
- Deroceras altenai Lupu, 1976 (synonym)
- Limax tunicata Gould, 1841 (synonym)