Did you know, as you hike or bike Mount Diablo in the rainy season, you may encounter a truly strange and imperiled mollusk underfoot? They are not at all common, but we recently found one on our monthly MDIA BioBlitz hike on Mitchell Canyon Road. The Button’s Banana Slug (Ariolimax buttoni), the banana slug found on and around Mount Diablo, has a status of Globally Imperiled, meaning it is at high risk of extinction or collapse due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors.

The Button’s Banana Slug is a fascinating creature! The species has a yellowish-tan hue and can be either spotted or unspotted. It is a detritivore that eats dead organic matter, but also eat plants (they are herbivores), as well as animal feces and mushrooms. Its mouth is on the bottom of its head with a tongue called a radula that is covered in microscopic teeth to help break down food. Get this: the slug excretes waste through the anus located on the side of its head!

Banana slugs are simultaneous hermaphrodites—meaning it has male and female sexual organs at the same time. However, sexually mature individuals can have no male reproductive organs, reduced male reproductive organs, or normal male reproductive organs. Those with normal male reproductive organs can mate either as a male or a female, or can perform both roles at the same time if mating as a pair. Or it can self-fertilize.  Speaking of truly strange: during reproduction, Ariolimax buttoni may engage in apophallation (no details here - you can look that word up if you like strange and can stomach it!).

When looking for food or a mate, Ariolimax buttoni moves via a foot on its underside that contracts and relaxes. It can glide over surfaces by producing a slime layer that aids in combating friction. The slime it produces deters predators because it is toxic and causes numbing to the mouth of organisms that attempt to ingest it.

So, next time you see a Button’s Banana Slug, you will be looking at a rare, exceptional slug!

-Dan Sandri