Don’t Lick the Banana Slugs

As the rain returns to accompany us through winter, so do the banana slugs. It’s not that they go somewhere else for the summer — can you imagine a banana slug migration at an average speed of four inches per minute? These creatures rely on moisture to stay alive, so during warm or dry spells they secrete extra slime, bury themselves in leaves, and go dormant in a process known as aestivation, the opposite of hibernation.

When not hiding from the sun, banana slugs spend their time sliding through the forest understory of the West Coast, where three different species are found between California and Alaska. In Washington we have only the Ariolimax columbianus, or Pacific banana slug. Of the banana slug species, it has the least vibrant yellow color and can look like an overripe banana with its black spots. The Pacific banana slug can also be identified by its unparalleled size. It is the second largest terrestrial slug in the world at 9.8 inches long, after a European species which can reach a foot long.

Banana slugs are known for their sliminess. Besides preventing desiccation, slime provides a surface that is both slippery and adhesive. Slugs use slime to glide easily across even the roughest gravel and to adhere as they make their way up a tree or a glass door. Slugs also use their slime as protection against predators. 

Most creatures avoid eating them because of the inconvenience of a mouth filled with goop. Anyone who has held a banana slug knows how difficult it is to remove slug slime from your hands. Wiping it off with a towel is the best way, since washing with water only seems to make it slimier. This is because the slime is made when dry granules called mucins excreted by slugs mix with water. The mucins expand up to 100 times, meaning when mucins meet saliva in a potential predator’s mouth, it ends up with a sticky mess.

Shrews, which are known to occasionally eat slugs, have been observed attempting to clean their mouths for up to an hour afterward. This is not a great use of time for a small creature whose metabolism requires it to eat constantly. Raccoons are known to roll slugs in the dirt to coat them before eating. Chocolate-covered banana, anyone?

Many a school child who attends one of the Key Peninsula’s local camps will know the other interesting fact about banana slug slime: It has a numbing quality. I have licked a slug, thanks to an irresistible challenge by my outdoor instructor in fifth grade, and I can attest that the numbing is real. This is also thought to be a defense mechanism, but as yet scientists have not discovered what causes this anesthetic feature. I have since learned it’s best not to touch or lick banana slugs for their sake, not ours, as they are not used to human soaps, perfumes or the oils on our skin.

Banana slugs are detritivores, meaning they play an important ecological role by eating decomposing matter and turning it into nutritious soil. They consume mostly fallen leaves, moss, lichen and animal droppings. Their special taste for mushrooms means that they often spread spores while cruising between meals. 

Slugs possess two pairs of tentacles, which can retract quickly and even regenerate if bitten off. The top pair detects light intensity, and the bottom pair is used for feel and smell. Stopping to watch a slug munch away is sure to amaze. They possess a special body part unique to mollusks called a radula. This tongue-like ribbon is covered in microscopic teeth that it uses to cut up its food. New teeth are constantly being formed to replace the ones that get worn down.

The banana slug is well-known in popular culture, although many new to the West Coast are baffled the first time they see one in person. It was adopted in 1986 as the mascot of UC Santa Cruz, and two years later, a group of young Camp Fire Girls in California started a campaign to have it named the state mollusk. The bill was eventually vetoed by then-governor George Deukmejian, who said that if the state were to select an official mollusk, it should be one “more representative of the international reputation that California enjoys.” It sounds to me like the governor didn’t do his homework about this incredible creature. Perhaps it’s time to show our own love for the slimy banana slug by making it the official state mollusk of Washington.

Nancyrose Houston is the Outdoor Environmental Education Director at Sound View Camp.

Nature Overlooked