A banana slug is a type of mollusk, with the classic soft body of a mollusk but no hard external shell. The animals are found in the forests of the Pacific Northwest, with the temperate redwood forests of Northern California proving a popular hangout spot for these slugs. In addition to providing clues to the evolution of mollusks, banana slugs are also the official mascot of the University of California, Santa Cruz. They also nearly became the California State Mollusk in the late 1980s.
There are several species of banana slug, all found in the Ariolimax genus. They are often yellow with brownish spots which cause them to look rather like bananas, although they also come in white, green, and brown. The animals prefer the damp environment of forest floors and gardens, where they feed on plants, fungi, lichens, and decomposing vegetable matter with their rasping mouthpart known as a radula.
The animals are infamous for very extremely slimy, and the slime is very persistent and difficult to remove. The slime serves a number of functions. The animals use the slime to lubricate the ground so that they are not injured by sticks and stones, for example. Slime also keeps the skin of a banana slug moist, which is important for gas exchange and breathing, and it discourages predators. In addition to the slime, these slugs also put predators off with a mild neurotoxin, which causes brief numbing.
Like other mollusks, banana slugs move with a single muscular foot, and they have a hump of flesh around their heads. The animals use two sets of antennae to communicate. One set, known as the eyestalks, are located higher on the head, while the lower stalks detect pheromones from other banana slugs. Both sets can be retracted for protection.
The yellow slugs are easy to spot in the dim forest, and they are often out in force after a rain. The banana slug is hermaphroditic, and it mates by exchanging sperm with another banana slug, in a process which can take hours. Each slug fertilizes its own eggs, and hides them in a damp place to hatch. Many people are enchanted by these slugs because of their intriguing color and seemingly curious faces, characterized by their gently waving eyestalks. Others, especially gardeners, dislike the animals, as they can be destructive to plants and they are quite unpleasant to handle or step on.