Brown Field Slug

Deroceras panormitanum

Summary 2

Deroceras panormitanum is a species of air-breathing land slug, a terrestrial pulmonate gastropod mollusc in the family Agriolimacidae. This article is about Deroceras panormitanumsensu stricto, which is now known to occur only in Sicily and Malta. Previous to 2011, this name was also applied to what turned out to be a distinct species, Deroceras invadens, a species which has spread around the world and is often a pest. Because this is a recent change in...

Distribution 3

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

Morphology 4

External: Mantle 1/3 body length; light to medium brown, gray, or black body, sometimes with dark brown flecks; long head and neck when extended; fairly translucent skin; mantle lighter in color than dorsum; pale edge of pneumostome; short keel with no spots; sole with distinctly darker coffee-coloured lateral zones and a cream zone in the middle (only the lightest specimens have a uniformly light creamy sole); clear body and sole mucus (Quick 1960; Kerney & Cameron 1979; Wiktor et al. 1994). Sometimes also black (in Bulgaria), brown, reddish or violetish.

Internal: 4.5 x 2 mm internal shell; dark ovotestis forwards on visceral mass; penis with irregular shape, anteriorly widened, a laterally swollen part has a rough surface and is glandular, posterior part of penis smaller and narrower, but variable; penis with 2-lobe appendix in a crescent-shape, with 4-5 digital flagella in the middle; penial retractor muscle usually forked with main connection point at base of appendix; stimulator conical, sometimes dark; rectal caecum minimal or absent (Quick 1960; Kerney & Cameron 1979; Rodriguez & Hermida 1993; Wiktor et al. 1994).

The slug is exceptionally variable in its genitalia (particularly penis), probably more than any other agriolimacid, obviously one of the bases for its success during its human-based artificial range expansion. There seems to be a general trend towards reduction of penial appendices.

Differs from D. laeve: is larger and even more active; in profile, tail tip is square-ish, while D. laeve tail is pointed; penis has two big lobes and digital flagella at its tip; and visceral cavity is dark in color (Quick 1960; Reise et al. 2005).

Eggs: 1.5 x 1.5 to 1.75 x 1.4 mm; up to 50 per clutch (Quick 1960)

Juveniles: 3 mm long, light and translucent, with purplish tentacles at hatching, with pigmentation then proceeding from the head and tail (Quick 1960).

Size 5

25-35 mm long extended (Quick 1960; Kerney & Cameron 1979); up to 20 x 4.5 mm (preserved), not different from numerous other Deroceras species.

Habitat 6

Habitat Type: Terrestrial

Number of occurrences 7

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

Estimated Number of Occurrences: > 300

Comments: In California, it is known from 5 counties: Alameda, Contra Costa, Los Angeles, San Francisco, and Santa Clara (McDonnell et al., 2009).

Behaviour 8

Active, aggressive species that can whip its tail. Often cannibalistic and aggressive to much larger slugs (Kerney & Cameron 1979; Rollo & Wellington 1979).

Very fast slug (Quick 1960).

Life cycle 9

Mates and lays eggs year-round (Quick 1960). Reproduction exclusively by copulation; life cycle short, up to 3 generations per year.

Sources and Credits

  1. (c) Paul Morris from USA, some rights reserved (CC BY-SA),
  2. (c) Wikipedia, some rights reserved (CC BY-SA),
  3. (c) NatureServe, some rights reserved (CC BY-NC),
  4. (c) (F. Welter Schultes); Paustian, Megan, some rights reserved (CC BY-NC),
  5. (c) (F. Welter Schultes); Paustian, Megan, some rights reserved (CC BY-NC),
  6. (c) NatureServe, some rights reserved (CC BY-NC),
  7. (c) NatureServe, some rights reserved (CC BY-NC),
  8. (c) Paustian, Megan, some rights reserved (CC BY-NC),
  9. (c) Paustian, Megan; (F. Welter Schultes), some rights reserved (CC BY-NC),

More Info

iNat Map

Establishment introduced
Slug or snail slug