Common Name: Pacific Banana Slug
Scientific Name: Ariolimax columbianus
Species: A. columbianus
Banana Slugs are Mollusks, which means they are soft-bodied with no visible skeleton. They also belong to the class Gastropoda, which can be recognized by having a muscular foot, a mantle with a cavity, a meaty hump on their back, and a radula or sand-paper-like grinding mouthparts. They are Pulmonates, which means they have a small lung inside their bodies which opens to the outside with a pneumostone.
Some of the first studies were conducted along the Columbia River; Giving it the species name A. Ariolimax columbianus. Gastropoda describes the banana slugs stomach-foot or muscular-foot, which allows them to slowly crawl on a series of muscular waves. Pulmonata describes their small lung that opens to the outside with a pneumostone, the hole slugs breathe through. The banana slug is the second largest slug in the world, growing up to 10 inches in length. On average they range between 6-8 inches, with a lifespan of 1-7 years. Their coloring is sometimes bright yellow, occasionally with black spots, or solid greenish. Individual slugs will change colors with alterations in food consumption, light exposure, and moisture levels. Color may also indicate whether a slug is healthy, injured, or what age they are. Their coloring allows them to camouflage with leaves and other debris on the forest floor. This serves as protection from such prey as beetles, raccoons, and even other banana slugs. That’s right, these funny critters are tertiary consumers. They are forest floor scavengers that feed on small (already dead) animals, but they are mostly decomposers, feeding on detritus. Banana slugs are considered general herbivores that eat all kinds of leaf litter, green plants and fungus (mushrooms are their favorite foods) and occasionally feed on animal feces and carcass. In the process of debris munching, the A. columbianus disperse seeds and spores while excreting a nitrogen-rich fertilizer. Slugs, at times, are also frugivores and may play a minor role in forest plant regeneration and seed dispersal.
Ariolimax columbianus, commonly known as the banana slug, is common to the Pacific Northwest region of North America due to the relative stability and isolation of these areas. They can be found in foggy moist forest habitats of southeast Alaska, British Columbia, Washington, Oregon, and California. They are continuously distributed throughout this region where they seek shelter beneath coastal redwoods and detritus. Within the primarily Mediterranean and Marine West Coast biomes, they remain active most of the year. Banana slugs show arboreal tendencies but are commonly encountered on the ground or within creek banks and tree roots during the dry summer months. They usually partake in nocturnal activity due to their high moisture dependency, but during the cooler rainy winter months, they are often seen during the day. They are stenotopic, meaning they have very specific preferences and limited ecological tolerance. Slugs are prone to desiccation, a complete or nearly complete drying out, such as may result in the formation of evaporites from bodies of water in an arid region. At one time banana slugs were blamed for damage done to redwood seedlings. A study later proved that a mutualistic relationship exists between the two. Banana slugs would rather eat cardboard than eat the seedling of a Sequoia. Instead, the slugs in the study ate other small plants which are redwood competitors for space, water, light, and nutrients. Rollo and Wellington found that A. columbianus often return to their shelters even if only inhabited for one night. Also, several slugs within their study alternated between to homes possibly displaying home range behavior. It is suggested that this homing behavior is conducive to slug olfactory senses. Slugs often disperse from sparse plant canopies to adjacent dense vegetation, but often will occupy less dense habitats to avoid competitors.
Slugs are hermaphrodites, which means they contain both male and female organs. A slug that is ready to mate will smell the slime trail left by another slug and follows the trail until it finds it. The slugs exchange sperm and produce 20 or less translucent eggs which is laid under a log or in leaves. Eggs are about half as big as your fingernail on your pinky finger and may be pearly white, pink or even yellowish. Mating and egg laying occurs several times throughout the year. Eggs and young are not protected by the parents. Slime has many functions. One is to keep the slug's skin moist so it can breathe through it. A slug breathes through its skin and just like the insides of our lungs, the skin must be moist to exchange gases. The slime gathers moisture out of the air like a sponge on damp days and out of the soil under logs on dry days. A second function of the slime is to protect the slug from predators. They simply hump up their body to make a bigger animal and produce a thick milky mucous. Most animals and birds do not like the slimey texture and the fact that it gets goey-er when it is put in their mouth. Also, when the slime comes in contact with a moist surface, it contains an anasthetic which temporarily causes the membranes to go numb. Raccoons will eat slugs but roll them in dirt first to bind up the slime. Garter snakes, ducks, geese and some salamanders will also eat them too. Baby slugs are eaten by shrews, moles and birds.Another function of slime is it is used in movement. Slime on the underside of a slug's body comes in contact with leaves and sticks on the forest floor. This slime coats the leaves, allowing the slug to move over, under and around them easily. A trail of slime is left behind it as it moves along. As well, a slug that has climbed a tree can get down quickly by dropping to the ground safely from a string made of slime.
Author: Dylan G.