Ariolimax columbianus

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Geographic Range

The Banana Slug can be found along the Pacific Coast. Its populations reach from as far north as Alaska to as far South as California. The heaviest concentration of the Banana Slug is found in California. (Branson 1996, Hill 1997)

Habitat

Banana Slugs live in the floors of forests in the Pacific Northwest. Because they respire through their skin, Banana Slugs require a moist environment to live. Banana Slugs serve as decomposers in forests. They break down plant materials. They also spread seeds and spores while eating. They spend much of their time during the day in moist, dark areas like under logs or other forest debris. (Branson 1996, Hill 1997)

Physical Description

The Banana Slug is the second largest slug. It can reach up to a length of 25 cm. The majority of Banana Slugs can easily be identified by their resemblence to a banana. They have yellow bodies with brown spots. Some Banana Slugs can be found with green, brown, or white bodies. The coloration of Banana slugs can change accordingly with their diet and the amount of moisture in their environment. The bodies of Banana Slugs have a muscular foot for locomotion. They also posses a hump on their back and a mantle. Banana Slugs have lungs that open to the outside through a pneumostone for respiration located on the right side of their mantle. Banana Slugs have two pairs of tentacles. The larger of the two pairs of tentacles are used to sense the brightness of light. The second pair are used to sense smells. The Banana Slug is able to retract both pairs of tentacles to protect them from the surrounding environment. Banana Slugs are covered with a slime that serves many purposes. (Branson 1996, Hill 1997, Murphy 1967, Nichols and Cooke 1979)

Reproduction

Like most slugs, the Banana Slug is hermaphroditic. This means that one slug has both male and female reproductive organs. Although they are capable of self fertilization, they more often cross mate. When a slug is ready to mate, it leaves behind a chemical in its slime to signal potential mates. Before mating, the slugs will eat each others slime. Mating usually occurs at night. The slugs exchange sperm that fertilize the eggs internally. The Banana Slug gnaws off its penis when disengaging from sex. Slugs are capable of storing the sperm that they have recieved for many weeks to fertilize eggs that are not yet mature at the time of mating. Banana Slugs produce up to twenty translucent eggs. The fertilized eggs are laid under logs or in leaves. The parent slugs play no role in the lives of their offsprings after laying the eggs. (Branson 1996, Hill 1997, Murphy 1967)

Behavior

One disitinctive behavior of the Banana Slug is how it gnaws off its penis when disengaging from intercourse. Another interesting behavior that the Banana Slug engages in is estivation. The slug buries itself in forest debris, secretes a protective layer of mucus, and becomes inactive. Estivation occurs during hot, dry periods to prevent the slug from dessication. Banana Slugs also hibernate when the temperature gets very low. (Branson 1996, Hill 1997, Murphy 1967)

Food Habits

Banana Slugs are herbivores. They eat leaves, dead plant materials, fungi, and animal droppings. Banana Slugs favor mushrooms over other foods. Banana Slugs eat their food using their radula. A radula is made up of many rows of teeth used for grinding up food particles. (Branson 1996, Hill 1997, Grzimek 1972)

Economic Importance for Humans: Negative

Banana slugs are sometimes viewed as pests by gardeners when they eat garden plants and flowers. (Hill, 1997)

  • Negative Impacts
  • household pest

Other Comments

The slime that the Banana Slug excretes serves many purposes. One function of the slime is for respiration. Respirtaion occurs partially on the skin of slugs. Gas exchange can only take place if the skin is moist. The slime also serves to attract mates to the slug. The third function of the slime is locomotion. The last function of the slime is for protection. The slime becomes an anasthetic when it comes in contact with a moist surface. This deters predators from eating the Banana Slug. (Hill 1997)

Contributors

Kristen Thomas (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

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.

ectothermic

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

References

Branson, B. 5/1/96. Snails Without Shells. The World & I, vol. 11: 166.

Grzimek, B. 1972. Grzimek's Animal Life Encyclopedia. Vol 3. New York: Van Nostrand Reinhold Company.

Hill, D. 1997. "Banana Slug" (On-line). Accessed 4/14/00 at http://www.naturepark.com/bslug.htm.

Murphy, R. 1967. The Larousse Encyclopedia of Animal Life. New York: McGraw-Hill Book Company.

Nichols, D., J. Cooke. 1979. The Oxford Book of Invertebrates. Oxford: Oxford University Press.