Arion ater rufus, also known as the red slug, large red slug, chocolate arion and European red slug, is a subspecies of land slug in the family Arionidae, the roundback slugs.

Description

thumb|left|[[Black slug (Arion ater) and Red slug.]]

Slugs in the genus Arion have the pneumostome (respiratory pore) in the front part of the mantle and a round back without a keel. Arion ater rufus is one of the largest species in the genus, up to 150 mm extended. As an adult it lacks the lateral bands found in many smaller congeners, but in some forms the sides are paler than the back. The body colour is often reddish, sometimes vividly so, but orange, yellowish, brown and greyish forms are also usual, and some individuals may be black. The foot fringe is vertically striped and is often a different colour than the back. The head and tentacles are often darker than the rest of the body. The mucus is sticky and colourless or orange. Externally the species is not reliably distinguishable from several other species, including A. ater and A. vulgaris, and can be difficult to distinguish from less closely related species such as A. flagellus, especially in the Iberian Peninsula where further similar species exist. His description consisted mainly of references to earlier published descriptions from around Europe. Recently a lectotype for A. rufus has been designated from amongst the specimens to which Linnaeus indirectly referred. This is a non-surviving specimen amongst those that Martin Lister described from Almondbury in West Yorkshire, England.

Arion ater rufus can be externally indistinguishable from Arion ater. There are anatomical differences between the taxa in their genitalia, but they hybridise, and so they have often been considered conspecific, particularly by British authors. appears to have been the first to describe the Continental form under a name other than rufus, so its name should be Arion ruber, Arion rufus ruber or Arion ater ruber. In Scandinavia and northern Britain the closely related species A. ater occurs in its place, but A. rufus has invaded parts of Scandinavia over the last 200 years. It is also extending its range further eastward in Europe, and even in eastern Germany it is possibly an old introduction. Arion ater rufus is also known as an introduction in North America. A related form, reddish in coloration but perhaps more closely related to A. ater s.s., has recently turned up in Turkey, on both sides of the Bosphorus.

Habitat

It is familiar from gardens and parks as well as disturbed agricultural landscapes, but also from a diversity of natural habitats including woodland, meadows, margins of water bodies, coastal habitat, and moorland.

Behavior

At rest A. rufus contracts into a hemispherical shape. When disturbed, it performs a rocking motion, sometimes for many minutes. This may take several attempts and sometimes is unsuccessful. Then the genital atria evert, and swell rapidly (1–2 min) to form a large, white, spherical mass between the bodies. The slugs remain like this for 90 minutes or longer, during which time a spermatophore is manufactured, filled with sperm, and in part passed over to the partner, hidden by the enveloping atria. Eventually one partner starts to become active, the configuration consequently rotates, the atria contract, and the genitalia separate. The spermatophores, anchored in the recipient's bursa trunk, are thereby pulled out of the donor's epiphallus. As the genitalia fully retract the spermatophore is taken in.

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Arion rufus 1650.JPG|Dark individual

Red slug (Arion rufus).JPG|Light individual

Rode wegslak (Arion rufus), 07-09-2024. (actm.).jpg|Copulation

Red Slug copulation.jpg|Mating

</gallery>

References

  • Arion rufus at Encyclopedia of Life (3 pages)
  • Arion rufus at Animalbase taxonomy, short description, distribution, biology, status (threats), images