Banana Slugs: Slime and all

banana slug
Banana slug (photo by Deb Hanson)

Oregon is home to one of the biggest land mollusks in the world – the banana slug (Ariolimax columbianus). These unmistakable creatures can grow six to 10 inches long. So named for its often yellow color with brown spots (though they can be green, tan or brown), banana slugs are common year-round residents and are often seen crossing hiking trails, especially at night or on rainy or high humidity days. They need a wet environment to help them breathe. Dry air causes their skin to dry out. They live mostly in wet forests with ample leaf litter.

I’m not sure why people do this, but I’ve heard that folks who lick a banana slug discover quickly that their tongues go numb and stay that way all day. Why? Banana slugs, cute as they are, have a mild poison in their slime (the mucus that covers their bodies) that repels potential predators, unless its a garter snake. Apparently garter snakes and Pacific salamanders are immune to the tongue-numbing slime of the banana slug.

That slime is important to the slug for a lot of other reasons. Being composed of mostly water and needing to breathe through its skin, the banana slug must stay moist. The slime that coats its body can absorb up to 100 times its weight in water, helping to keep the slug moist and preventing dry air from turning it into a shriveled up clod. (That’s also why it’s hard to wash slug slime off your hands. It’s better to wipe it off with a dry towel first.)

Banana slug slime also acts as a lubricant, making it possible for them to slide across soil and over sharp objects – even a razor blade – without getting cut. Simultaneously, it serves as a glue, helping them stick to smooth vertical surfaces like window panes. Some snakes have even been found with their mouths stuck shut with slug mucus! Now, that’s sticky. Slugs use their slime trails to find each other during mating season.

Perhaps the most intriguing  banana slug behavior occurs during mating. Slugs are hermaphrodites, meaning the same slug has both male and female sex organs. They perform an elaborate and prolonged mating ritual, including biting and head- and tail-bumping. They also have penises that are longer than their bodies. When mating, both slugs will insert their penises into each other to deposit genetic material – sometimes this takes hours. Occasionally, they get stuck together and cannot retract their penises. If this happens, the slugs will engage in apophallation (meaning they chew their penises off) to dislodge from each other. Ouch!

Take a close look at a banana slug and you will see a hole in the slug’s side. That hole is a pneumostome, which connects to their lungs and helps them respire. You may also notice the banana slug has two sets of retractable tentacles on its head. One pair is used to sense bright light. If you look close enough you can see a dark spot on the end of each of these long tentacles. Those are the eyes. The second shorter pair of tentacles are used for feeling, smelling and tasting. Banana slugs are generally herbivores, but eat fungi and animal droppings, too. Their favorite food is mushrooms.

The next time you are walking in a wet Oregon forest, be on the lookout for the slime trails and squishy bodies of these remarkable creatures. Take a moment to get down on their level and watch them move. See the forest from the slug’s point of view. You may be surprised at what you find.

And if all that grosses you out, maybe you just need to sing this song written by Steve van Zant and the Banana Slug String Band!

Have you seen a banana slug? Where, and what color was it?


3 thoughts on “Banana Slugs: Slime and all

  1. Tracy

    Yes in deed i did and had to post it on line because i didn’t know what it was. I’ve seen banana slugs but only all yellow, this one was brown looked like a rattle snake had been eaten and it’s head with half a body was left and that’s what made me notice it. Then i bent down to really see and it was alive and moving with a billion lil leg type things moving it across the wet grass it’s color was just for camouflage and it was amazing to say the least i was intrigued by it’s everything! I would live to know are those legs or did it just look like it?? I wanted to show a picture but couldn’t post on here. It was brown tan with big black spot on top of first segment next body part had a lot of spots and lines going all the way down it as the head segment was super smooth slimy and had no other marks. Amazing creatures! I love all of nature.


  2. Brandon

    Very well written thano ypu fpr this i read thos to ancer my son’s question 9n slugs after twlling him all about the banana sulgs using the information from ypur writing my son says. Dad your my best friend hes 4yr old. An know about slugs


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