Slugs – A Tale of Gnawing on Morning Wood

Hey you, let’s talk slugs! Yes, I said slugs! What if I told you, that one species of banana slug, Ariolimax dolichophallus, in Latin, literally means “long penis”. Not only that, some species of slugs chew off penises. Intrigued or grossed out? Well, keep reading and be prepared to be pumped full of slug knowledge.

So why am I talking about slugs? Well on a cool, foggy, drizzly morning, I took a short walk through an area of beautiful temperate rainforest near the Bamfield Marine Sciences Centre. The forest contained enormous fir and cedar trees that provided a home to many animals including slugs! The slugs in the forest enjoy gnawing on things found on trees and on the forest floor such as lichens, moss, mushrooms, leaves, and dead plant material.


Notice the breathing pore (the pneumostome) found on the right side of the head.

I encountered a few slugs on and near the path during the walk. No, it’s not because they’re super adventurous and like to lounge around in the middle of open walking paths, but because the eyes on most slugs are very simple and can only distinguish light and dark.

I took a close look at these slimy looking creatures that look like snails without a shell (in fact, most slugs evolved from snails), and noticed a large hole on the side of the head of the slug. This hole, called the pneumostome is present in both land snails and slugs. The pneumostome is used for breathing air and the opening leads to a single lung. In slugs, it can be easily identified, as the area where the pneumostome is located is not covered by a shell, like it often is in snails.

Ok, let’s talk slug reproduction. Slugs are hermaphrodites, meaning they have both female and male reproductive organs. When two slugs mate, they circle and wind around each other and may exchange sperm with each other. In some species of slugs after mating, one or both individuals may chew off the other’s or their own penis. You may think the slug who had his penis removed really got shafted as he can’t go on to reproduce with others. However, one theory is that it is actually advantageous as the chewed off penis will remain in the slug and will prevent the slug from being able to mate with other slugs. From one slug’s perspective, what a dick move. From the other slug’s perspective, a smart sacrifice. Another theory is that mating results in the penis being stuck inside the body of the partner and the only way to separate from each other would be to chew off the penis.

Slugs are important to the temperate rainforest ecosystem as they help to break down dead organic matter but they are also a source of food for animals like birds and snakes. Next time you take a walk through the forest, be careful of where you step as these slugs play an important role in the ecosystem!


A heartwarming video of two mating slugs:


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