Banana Slug - Ariolimax columbianus

Banana Slug 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 mouth parts). They are Pulmonates, which means they have a small lung inside their bodies which opens to the outside with a pneumostone.

Banana Slugs are the second largest slug in the world, growing up to 25 cm long. They are so named because very often their coloring resembles a banana, bright yellow body with black spots. Solid greenish, pale brown and even almost white specimens can be found locally too. They can change their color slightly over time, becoming more intense or paler as the light, moisture and food allows. These colors help them to camouflage with the leaves on the forest floor.

The Banana Slug lives in moist forest floors along the Pacific Coast of North America from California to Alaska. It is a decomposer, which means it chews up leaves, and animal droppings and other dead plant material and recycles it into soil. One of their favorite foods seems to be mushrooms. In the process of eating, they also spread seeds and spores.

With only one muscular foot, a slug moves slowly. How it moves can be seen when you place a slug on a piece of glass and look at it from underneath. Small horizontal waves of muscle move from the back to the front of the animal, allowing it to glide over a surface. A slug can travel over a razor blade or sharp edge of glass without cutting itself because of the slime that covers the foot.

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.

Slugs use their two pairs of tentacles to sense their environment. The larger pair at the top of their head have a small black spot at each tip that are used to detect light. Slugs cannot see images like we can, but instead rely on brightness or darkness to tell them which direction they should move. They also have a second pair of antennae located at the lower front of the their body. This pair acts like a nose, picking up chemical smells. Both of these tentacles can telecope in and out as they move along the forest floor to protect them from damage when they bump into leaves and twigs.

Sometimes as a slug is moving, you will notice a small hole, usually on its right side, near the front of the body. This hole is called a pneumostone. Air enters the hole and passes into a small lung-like cavity. Like us, when a slug is exercising hard (moving quickly), it needs more oxygen in its body. This extra lung provides more skin area for the slug to breathe through.