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Slug Fest

Written by Shannon Finch | Published on June 22, 2015 | Filed under Humane Connection
The content that follows was originally published on the Institute for Humane Education website at http://humaneeducation.org/blog/2015/06/22/slug-fest/
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banana slug

Native banana slug, Ariolimax columbianus

by Shannon Finch

Slugs. Even their name sounds, well, “ugh.” I’ve never met a gardener who had a kind word to say about them, but slugs are important as scavengers and recyclers.

I confess, I find slugs fascinating. They are hermaphrodites, having both male and female sex organs. They can alter the stickiness of their mucus, enabling them to glide easily on all kinds of surfaces — including poky things like gravel, or to stick on a vertical surface.

Their slime trails are maps they follow back to their burrows or to particularly good food sources. They pulverize their food with their radula, an appendage outfitted with thousands of sharp teeth. As with sharks, these teeth are replaced as they wear down. They can eat up to 40 times their weight every day.

I’m tolerant about the occasional slug in the garden or the flower beds. This spring we’ve had unusually warm temperatures, which, coupled with our notorious Pacific Northwest moisture, has led to a slug population explosion. And they’ve turned their little radulas on my new rain garden.

To make the garden we diverted water off our roof, down a rain chain into a shallow depression planted with native plants that don’t mind having wet feet. The garden filters the water, releasing it slowly back into the environment. It provides habitat for all sorts of creatures, including—ahem—the slug.

Chocolate arion slug next to a quarter

Brutus, a chocolate arion (Rufus arion) next to a quarter

Our native banana slug is not the problem. It’s the non-native chocolate arion (Arion rufus) that goes for new plants in particular, decimating my western columbine, lupine, and purple coneflower. They also adore yellow and pink monkey flower but don’t care for the scarlet monkey flower. Go figure.

The typical solution is to poison slugs with baits containing metaldehyde, which dehydrates the slugs, killing them. Metaldehyde doesn’t discriminate, and many other creatures, including birds, amphibians, dogs, and even humans can die from ingesting it. Baits containing iron phosphate are considered safer, but there have been a couple of studies that show it might harm earthworms. Moreover, I am not comfortable knowing that it can take three to six days for the slug to die after ingesting the bait. It would be kinder to kill them outright.

Many gardeners do spear or slice slugs up. I don’t have the stomach for that. Beer traps are another alternative but are messy, and of course the slugs drown. I didn’t want to kill them for just doing what slugs do, nor did I want to make them suffer in any way; but my frustration was rising to an irrational level. In a weak moment, I actually had a bottle of Sluggo in my hands. My husband said, “You know you don’t want to do that.” I sighed and put it back on the shelf.

Hut with added copper bracelets

Hut with added copper bracelets

I first tried garden lime around the plants. The thinking is that slug bodies are acidic, and the lime makes the soil more alkaline, theoretically deterring slugs. My slugs didn’t get that memo: within minutes they crossed the lime circles to feast on sunflowers.

I then made protective huts out of milk jugs and juice bottles I begged off my neighbors. I cut the bottoms out and slipped the bottles over the plants. These work fairly well, but check to make sure no slugs are burrowed under the soil, because otherwise you’ve just corralled them in with your plant. An important note: when using the huts, they need to be slightly buried into the soil. Slugs are very strong for their size and have no problem pushing one of those up.

The huts act like greenhouses, so leave the cap off for air circulation. Ambitious slugs can crawl up the container and down through the hole, so as an alternative, you can leave the cap on and punch some smaller air holes in the bottle. Yes, the huts look a little weird. But they can help you get the plants large enough that they become less palatable and more able to withstand some occasional munching.

I also found a product called Slug Shield™, which are woven copper barriers. The website says it works by causing an electrochemical reaction—like an electric shock—when the slug comes into contact with the metal. I ordered mesh “bracelets” that wrap around the plant stems, and a wider barrier mesh for the garden.

copper wire around plant

copper wire barrier around a plant

On slug patrol the morning after we installed the perimeter barrier, I found a large one nestled up between the garden bed and the barrier. Technically it* wasn’t in the garden, but it didn’t appear to be getting shocked, more like massaged. As I mulled that over, a cute baby slug traveled right through one of the minuscule mesh squares and easily across the barrier.

With gritted teeth I emailed the company for an explanation. The owner said that the slugs needed to hit the barrier with their tentacles, so he suggested that we bend the perimeter barrier at the top and bottom. As for the little ones, he said they get through everything.

Other things you can do to deter slugs:

  • Water in the morning, and just the plants, not the surrounding ground.
  • Remove old boards, pots, and debris, all places where slugs like to hide.
  • Before planting, rake the area to expose any eggs, which will then desiccate.
  • Handpick. I plop them into a bucket and carry them far into the woods; some slugs can travel as much as 40 feet in a night. (Wear gloves. If you do get slimed, don’t try to wash it off, you’ll just make it worse. Slug slime is hydrophilic, meaning it’s activated by water. Cut it with some vinegar, wipe with a dry cloth first, or rub your hands briskly together so that it forms a ball.)

I don’t want to get rid of every slug; I just want them to leave a little for me. The bracelets have worked for many plants, and the perimeter barrier around the garden seems to be working so far. I’m still using huts, stuffing a copper bracelet in the hole for insurance. And I’ve given up on having some plants in the rain garden; the columbine and monkey flower now reside in pots on my deck.

*Because slugs are hermaphrodites, I am comfortable using the pronoun “it” when referring to a single slug.