The commonest slug in NW Europe (Kerney & Cameron 1979) and the major pest slug in agriculture, worldwide.

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.

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) It has a wide global distribution and is found in most temperate and subtropical regions (Roth and Sadeghian, 2003) including Asia, Australia, Canada, Europe, New Zealand, the United States, South Africa, South America, and islands of the Pacific and Atlantic Oceans but its native range is thought to be western Europe (Forsyth, 2004).

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).

Up to 40-60 mm long (preserved 25-30 mm); varies in size according to the habitat.

Brown, grey or creamy coloured, usually with some darker spots. Grows up to 5cm. Has a keel, or raised ridge, on rear third of body, and has the pulmonary aperture in the rear of the mantle, on the right-hand side.

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).

Habitat Type: Terrestrial

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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).

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: Multiple species of Deroceras spp. were recorded in eastern Maine (11 of 101 sites) from litter samples in a variety of habitats (Nekola, 2008). In New York, Hotopp and Pearce (2007) report it from 7 counties in central and southeastern regions as introduced It was documented recently in southeastern Wisconsin (Jass, 2006). In California it occurs in 24 counties: Alameda, Butte, Calaveras, Contra Costa, Del Norte, Los Angeles, Marin, San Bernardino, San Francisco, Tulare, Santa Clara, Ventura, Humboldt, Imperial, Kern, Monterey, Sacramento, San Luis Obispo, Shasta, San Mateo, Santa Barbara, Santa Cruz, Sonoma, and Riverdale (McDonnell et al., 2009). It had been documented historically in Colorado (Cockerell, 1927) as Agriolimax agrestis. Forsyth (2006) documented introduced populations at Lac des Arcs, Alberta and museum records from Waterton Lake National Park (verified anatomically). Forsyth (2005) documented it in the Upper Fraser Basin of central British Columbia at an abandoned farm site, roadside highway pullouts, and a provincial park but is widely introduced in the rest of British Columbia; including one site (along a lake shoreline near Mackenzie) in the Peace River- northern Rockies region (Forsyth, 2005). Most recently, it was discovered in the Ktunaxa Traditional Territory in southeastern British Columbia (which extends from near Canada - U.S. border north to about 50 km north of Cranbrook) (Ovaska and Sopuck, 2009).

>1,000,000 individuals

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).

Not aggressive (Rollo & Wellington 1979); aggregations occur with bad moisture and temp levels (Rollo & Wellington 1981). Homes to shelter (Cook 1979).

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).

Deroceras reticulatum is partly freeze-tolerant (experiences mortality at or below -4.7 C for 30+ min.) (Cook 2004).

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: G5 - Secure

Reasons: It has a wide global distribution and is found in most temperate and subtropical regions (Roth and Sadeghian, 2003) including Asia, Australia, Canada, Europe, New Zealand, the United States, South Africa, South America, and islands of the Pacific and Atlantic Oceans but its native range is thought to be western Europe (Forsyth, 2004).

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.

Global Short Term Trend: Relatively stable (=10% change)

Global Long Term Trend: Increase of 10-25% to decline of 30%

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.

Comments: Deroceras reticulatum was until recently included under the name Agriolimax agrestis (Linnaeus, 1758) in older literature. Deroceras agreste, however, is a separate species and records of D. agreste in B.C. probably refer to D. reticulatum (Forsyth, 2004).