Natural Connections: Slugs

"Dampness cooled my fingers as I lifted softened wood out of the limp maple leaves."

Natural Connections: Slugs

These damp, gray days of fall can get a little dreary sometimes. When I don’t have time for a big hike, I take my camera for a walk along my driveway. Strolling slowly, I let my focus soften as I wait for something to catch my eye. Earlier this month, a lichen-covered stick, brought to earth by precursors of the gales of November, made me pause.

Dampness cooled my fingers as I lifted softened wood out of the limp maple leaves. In order to make sense of the small log, I assumed the hunched posture of nearsighted people everywhere. My field of vision narrowed, and I became immersed in an alien world. Orange, gray, brown, yellow, wrinkled, dusty, lumpy, smooth, round, and branching, the variety of shapes and colors colonizing this stick were dazzling!

In various outdoor teaching resources, I’ve read about an activity called a “micro hike,” where students are given a short string and told to blaze an ant-scale trail across the forest floor. Although I have a baggie full of yarn strands in my teaching tools, I’ve never found the time to pull them out. Now, both my eyes and my camera bushwhacked across the lichen-covered barrens of the stick, forging a path of discovery.

Suddenly, something wet and shining loomed ahead. As I watched, the slug extended their beige-colored form and undulated across the lichen field on their single, body-length foot. Their movement was surprisingly graceful. When I looked up the species, the name was lovely, too: dusky arion. Never mind that they are introduced from Europe and often become garden pests. I’ll resist judgement if they resist my tomatoes.

Slugs don’t see the world; they touch, and smell, and taste it. The four dark tentacles—two short ones down low, two long ones on top—stretched and explored with delicate fascination. Using pale, glossy lips infused with chemoreceptors, the slug gently touched and recoiled from the lichens’ wrinkled surfaces. Yeasts sometimes join the lichen partnership and produce antifeedant chemicals to repel herbivores. The slug’s lips may have been sensing those.

A few times, the slug seemed to pause and gum the lichen, like a toddler trying a new food. Were they using their sandpaper-like tongue called a radula to scrape up algae who had colonized the lichens’ many surfaces?

When that slug reached the end of the stick, I put them down and picked up another section of the fallen branch with yet another slug glued to its surface. This slug wasn’t traveling, but they were moving. The slug squeezed and contorted their whole head region, and opened and closed a hole in their side. Out of that hole snaked a string of mucus with little brown dots suspended within. Slug scat!

The scat was extruding from near the slug’s head, and there’s a perfectly reasonable explanation for this. Slugs are evolved from snails, and a snail’s anus must be located far enough forward on their body to easily get the poop outside of their shell. The trait has carried through.

Why would a slug get rid of the beautiful, cozy, humidity-controlled, predator-resistant house that snails still possess? Shells require a lot of calcium to build, which is in short supply in our sandy soils. Shells also prevent their owner from squeezing into hiding places like soil tunnels and rotting logs, two habitats that contain enough moisture for a slug to survive. The loss of a shell broadens a slug’s options, and in the Arion genus, all that is left are a few calcareous grains under the rear of the mantle.

Laying that slug and stick back on the ground, I picked up a new one. This slug was resting even more tranquilly. Only their pneumostome (which translates to “air-mouth”) moved. The small, football-shaped holed opened to let in air, then slowly closed, then opened again. When a daddy longlegs explored too close and stepped on their mantle, the slug squeezed their pneumostome shut as we might scrunch up our whole face in response to a tickle.

These first three slugs were all roughly an inch long, but farther down my driveway the whimsical yellow cap of an Amanita mushroom caught my eye, and on its creamy white stem were three smaller slugs, half as long and much more slender. Babies! An individual slug, at least in the Arion genus, lives about a year. Eggs hatch before winter and they hibernate as teenagers, then become active early in spring—in the mirror image of this cool, damp weather—to finish growing up. Slugs are hermaphroditic. When they find a partner, they each inseminate the other and both lay eggs. Then, often, they die.

Standing to straighten my back, I was surprised to find how short my walk had been. Having explored through the exotic tufts of lichens and mosses, and observed these alien creatures, I felt like I’d been in another realm. And soon, those slugs will be entering another world I’m curious about. As they make plans to spend the winter hunkered down beneath the snow, I’m making plans to follow them into the Subnivean Zone. I’ll be sure to tell you what we find.

For videos of these three slugs, check out the Natural Connections Nuggets playlist on the Cable Natural History Museum’s YouTube Channel.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our exhibit: “The Northwoods ROCKS!” is open through mid-March. Our Fall Calendar of Events is ready for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Last Update: Oct 18, 2023 12:19 pm CDT

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