The second largest land slug in the world, the banana slug (Ariolimax columbianus) lives in dense, damp forests on the western side of the Cascades and Sierra Nevada from Alaska to central California. Although preferring a forest habitat, banana slugs can be found in more urban settings. Slugs and snails are members of the gastropod family of mollusks.
Banana slugs exhibit a wide range of color from white to black and all shades of yellow to brown in between. Sometimes it is splotched with a dark brown or black color. Its shape and the yellow color it often exhibits give the banana slug its common name. On the anterior end the banana slug has two sets of tentacles which sense the environment, the upper “eyeballs” detect light and movement while the lower set detect chemicals. The tentacles can retreat and extend to avoid perceived danger and damage. Banana slugs have a single lung connected to the exterior air via a pore called the pneumostome. A fleshy membranous covering on the anterior end of the slug secretes a slime or mucus. On the under surface of this mollusk is a muscular organ (the foot) which the slug uses to crawl or to rest.
The slime excreted by the mantle contains pheromones, chemicals that trigger responses in other members of the same species. Pheromones serve a variety of uses in organisms including alarm warnings, marking food trails, and as a sexual attractant. In slugs the mucus also provides a surface to facilitate locomotion, as well as protection from dehydration.
Banana slugs can estivate or enter a state of dormancy characterized by inactivity and a lowered metabolic rate. When temperatures become high or conditions are arid, banana slugs cover themselves with slime, dirt and leaves and estivate until the environment improves.
As hermaphrodites (each slug has both male and female reproductive organs) either partner can be the male or the female. After mating, which occurs throughout the year, the eggs are laid in logs or on leaf detritus. After laying the eggs, the slug has nothing more to do with its offspring.
Although mushrooms are the favorite food of banana slugs, they are not fussy eaters, ingesting living or dead plants, animal carcases, animal feces, lichen – almost anything. In turn, banana slugs are food for snakes, snails, foxes, porcupines, raccoons, salamanders, crows and ducks along with other predators.
A host of parasites infest banana slugs. Mites live in the slime of banana slugs. In fact, there is one mite that is only found in banana slug slime. Flukes, roundworms, tapeworms and other parasites also use the banana slug as an intermediate host.
This banana slug was photographed in the old growth forest along the North Umpqua Trail in Oregon.
One other factoid: the banana slug is the mascot of the University of California at Santa Cruz. Go slugs!!