Slugs
Arion rufus [picture: Guillaume Brocker]
Slugs are snail's shell-less relatives. Over time, some snails evolved and their shells became smaller and smaller until eventually the shell was enveloped by the mantle. Snails like Vitrina pellucida are at the intermediate stage, where the shell is disproportionate to the body, and they cannot recede into the aperture.
Vitrina pellucida (Müller, 1774)
Testacellidae slugs have a tiny fingernail-like shell stuck to the back of their body. This protects the mantle cavity, the heart and the kidney.
Testacella haliotidea (Draparnaud, 1801)
Some slugs have a tiny shell underneath the mantle (e.g. genus Limax) or some have reached a stage where there are only small calcium fragments under the mantle (e.g. genus Arion).
The main advantage to having no shell is speed: snails are obviously very slow, but slugs are much faster, so they can locomote faster to reach food or shelter. Also, without the shell, they can fit into smaller spaces. The disadvantages are that there is no shell to provide protection from predators and extreme weather conditions. Some slugs are poisonous to discourage predation.
Slugs on average are much larger than snails. The largest species is Limax cinereoniger, which can reach 30cm when extended. Slugs are almost as widespread as snails, but there are fewer species, and they cannot survive extremely harsh environments. Slugs can be a great pest because of the variety and amount of plants they consume. Slugs can be kept as pets, and care is similar to snails, but you must be more careful about preventing them from drying out.
For an identification guide to slugs of the British Isles (pdf format), click here.
Family Limacidae:
These slugs have a mantle which looks as though is has a fingerprint on it. There is a tiny shell underneath the mantle, which can be felt. These slugs have thin slime and can move relatively fast. They originate in Europe.
Limax cinereoniger
(Wolf, 1803):
[picture: Kevin Davies]
The largest slug species on Earth. The body colour is usually dark grey or black, but can be much lighter. There is usually a white stripe extending down their back.
[picture: Clemens M. Brandstetter]
The underside of the foot (above) is white with a dark edges. They eat fungi and plants and reside in woodland in northern Europe. Size: 200-300mm
Limax maximus
(Linnaeus, 1758):
[picture: Kevin Davies]
This slug is known as the Leopard Slug, for obvious reasons, although body pattern can vary a lot. This slug can be carnivorous, but it rarely eats other gastropods, preferring fungi and plants. The mating is very spectacular. The two slugs hang from a rope of slime one metre long, and curl around each other, mating for several hours in mid-air. They live in many habitats all over Europe. Size: 100-200mm
Limax flavus
(Linnaeus, 1758):
[picture: Kevin Davies]
This slug varies in colour - it can be green, yellow or grey. It is covered in many pale spots and has blue antennae. Feeds on many types of plant and fungi. Resides in gardens, parks, etc. In Southern and Western Europe. Size: 70-100mm
Family Arionidae:
Ariolimax columbianus (Gould, 1851):
[picture: Thomas Schoch]
This is one of the three species of 'Banana slug' that live in North America. A. columbianus has a ridged back, and varies in colour from bright yellow to green, olive, and even blue. They live on the East Coast of America, all the way up to Alaska. They grow up to 250mm.
Arion ater (Linnaeus, 1758):
Can reach 150mm when extended, and has thick, sticky slime which is difficult to remove (don't use water). When contracted they sometimes rock from side to side, to confuse predators. A. ater are scavengers with a hugely varied diet (carrion, faeces, plants, fruits, vegetables and more).
[picture: Kjetil Lenes]
They are usually black or brown but can be grey or even white (above). All over Europe in many habitats.
Arion rufus (Linnaeus, 1758):
[picture: Kevin Davies]
Arion rufus and Arion ater are very similar slugs. The only difference is that A. rufus is orange or orange-brown with an orange border around it's foot (and a more slender genital atrium). Some consider A. rufus to be a subspecies of A. ater.
Geomalacus maculosus (Allman, 1846):
This slug is very beautiful. The body is black with white spots. It feeds on plants and lichen. This slug is unique because it can roll itself into a ball. They live in Brittany, north-west Spain, northern Portugal and south-west Ireland. Size: 55mm.
Family Trigonochlamydidae:
Selenochlamys ysbryda:
[picture: Kevin Davies]
This species was discovered very recently in south Wales, and named in 2008. It is thought to have been introduced; its closest relatives are native to eastern Turkey and Georgia. The species is 60-70mm in length and the body is completely white, with vein-like markings down the body. It has no eyes, and is thought to have evolved in caves. The pneumostome is located at the rear end of the body. They are carnivorous, and spend most of their time underground feeding on earthworms with their specially adapted radula. The teeth of the radula are much longer and sharper than those of herbivorous species. For more information on S. ysbryda, click here.
