I was quite surprised to discover this morning that I have only ever written one post on slugs — and it was a fake April Fool’s post on Homing Slugs. Let’s be honest, slugs are nasty, ugly creatures, so I can understand why I have avoided them up to this point. Still, I feel bad that I haven’t taken the time to give slugs their due. After all, they can’t help the way they look.

I’ve always known that banana slugs were a thing, but knew absolutely nothing about them (I assumed they vaguely resembled bananas). There are actually three species of banana slug, all of which can be found in North America. They make up the genus Airolimax, and are the California banana slug, the Pacific banana slug, and the slender banana slug. They range up and down the west coast, from southeastern Alaska to California.

Banana slugs are quite slug like, being long, fat, and covered in slime. They are large slugs, with the Pacific banana slug reaching lengths of 25 cm and weights of 115 grams (making it the second largest terrestrial slug in the world). Their name comes from the slugs’ bright yellow colour, but not all banana slugs are yellow. They can be green, brown, or white, and can be covered in a numerous black spots. They also change colour based on their diet, light conditions and moisture levels.

A spotted banana slug, which gives the poor thing the appearance of an old banana.
Image by Thomas Schoch, CC BY-SA 2.5, via Wikimedia Commons

Like most slugs, banana slugs have prominent eyestalks that are used to sense light and movement. When I was a kid, I had great fun poking slugs’ eyestalks and watching them retract into the slugs’ heads. The stalks do this to protect themselves, but the slugs have a backup plan: if a stalk is bitten off (hopefully by a predator, and not an overly curious child), it can be regrown. Slugs have a secondary set of tentacles, placed on the ‘chin’ of the head, that detect chemicals in the environment.

Breathing in slugs is quite interesting; the slugs have one lung, and don’t breathe through their mouths. Instead, they have what is called a pneumostome, which opens into the lung so the slugs can breathe. Slugs need to stay moist, which is why they are so slimy. The secretion of the slime prevents them from drying out. If environmental conditions are too dry, banana slugs can enter a kind of hibernation. They cover themselves with even more mucus and then snuggle under dirt and leaves until things outside their nest get wetter.

A really neat picture of a banana slug and its pneumostome. Image by Steven Pavlov, CC BY-SA 3.0, via Wikimedia Commons

Banana slugs eat dead things, and they aren’t picky. They will eat dead plants, animals, and fungi. Slugs mouths are weird; they have teeth, but instead of being in gums, the teeth are on the slugs’ tongues. They use this strange device to grab and eat their food.

Another very odd thing about slugs is their reproductive habits. They are hermaphroditic, with each slug possessing both female and male genitalia. Banana slugs can self-fertilize, but prefer to find a mate if possible. When they are in the mood, the slugs secrete a special chemical that attracts other slugs. In a particularly disgusting ritual, the slugs eat each others slime before engaging in intercourse. And once they’re done, the slugs bite off their own penises to disentangle from copulation. Slug sex is pretty nasty stuff.

I thought that after I wrote this post I would think that slugs are less gross, and maybe even less ugly. I was wrong. But I do have a greater appreciation for these guys. The have some pretty weird… stuff that they have to deal with.

Cover image from Wikipedia, Public Domain