Arion ater

Geographic Range

Arion ater is a terrestrial slug, common in England and the Pacific Northwest. (BBC 2000).


Arion ater prefer grassy fields and crops of vegetation. Strictly terrestrial, they typically live in moist, cool soil (Long 1999).

Physical Description

Although thought to be shell-less snails, Arion ater do have disc-type shells embedded in their mantle. This is surrounded by a fleshy oval tissue on their back. Slugs move about via a foot that, when flexed, allows the slug to control its movement.

Most Arion ater are orange when hatched, have a "straw" coloration until aproximately one inch in length, and eventually take on a black coloration. Typical slugs are about six inches long at maturity. (Branley 1996).


Although Arion ater are hermaphroditic, they do engage in cross-fertilization when a mate is available. After copulation, the slug may lay 20-50 eggs in crevices made in soil or in the cracks of decaying wood. These eggs typically hatch in six weeks (BBC 2000).


While relatively dormant during the day, slugs rely on the coolness of the night to search for food. Soil surfaces must be moist for slugs to safely move around. In fact one practice of gardeners is watering their plants early in the morning so that the ground is not so moist at night, when slugs are active. This is particularly useful when combatting Arion ater--considered the most destructive species of slugs (Long 1999).

Food Habits

Arion ater spend most of their time eating. This is done with an enclosed radula that contains transverse rows of sharp teeth. The slug's diet consists mostly of fungi and plants, but is occasionally supplemented by worms, insects, decaying vegetation, and feces. Slugs feed mostly at night when conditions are cool and moist (Long 1999).

Economic Importance for Humans: Positive

In general, slugs are crucial to a healthy ecosystem. They work to recycle decaying food and fecal matter that is then processed back through the soil. Without slugs working in such a manner, soil could potentially lose many of its nutrients (Nickel 1998).

Economic Importance for Humans: Negative

Slugs are often a nuisance to horticulturists because of their choice of diet. Lettuce is a crop that is heavily damaged by slugs. Any sort of vegetation is at risk to slug damage. Arion ater is considered to be among the most destructive of the slugs (Long 1999).

Conservation Status

This species is given no special conservation status.

Other Comments

Slugs have very few natural predators. The mucus that they secrete leaves the slugs sticky and slimy, and is thought that the mucus is highly distasteful. Among the slugs' natural predators are the hedgehog, badger, shrew, mole, mouse, frog, toad, snake, carnivorous beetle, and some birds (Nickel 1998).


Angela Stroud (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


reproduction that includes combining the genetic contribution of two individuals, a male and a female

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


February 2000. "BBC Education:" (On-line). Accessed February, 23 2000 at

Branley, A. 5-1-96. Snails Without Shells. The World and I.

Long, .. July 1999. Ultraeasy Slug Solution. Organic Gardening, 46:11.

Nickel, .. June 1998. The Slimy, Yet Special Slug. Natural History, 107:18.