Everything You Always Wanted to Know About Slugs, But Were Afraid to — well, o.k., maybe you didn’t really want to know this much about slugs…

by D.A. Salazar, MG Class of 2009

drawing of a slugWe master gardeners get a lot of questions about slugs. Mostly along the lines of “Yuck! Gross!” — which, granted, are not actually questions, but do convey a certain puzzlement about these particular molluscs.

Since they’re such an unavoidable part of our gardening lives, maybe it’s worth knowing a little more about them. Here, then, for your edification a brief general overview of the biology and habits of slugs, and the top WSU-approved recommendations for dealing with them in the home garden.

Slugs are pulmonate land gastropods. Pulmonate meaning they breathe air through a simple lung rather than gills. Gastropod translates as “stomach-foot” and is rather a misnomer, dating back to when humans thought slugs and snails crawled on their bellies. Actually, their digestive systems are on their upper (or dorsal) sides.

Slugs (and snails) comprise the largest class of molluscs. Which means they beat out all their cousins in the population race — including squids, octopi, cuttlefish, oysters, clams, nudibranches, geoducks. (And what a family portrait that would make.) According to WSU, one study done in the Pacific Northwest estimates that for every slug you find, there are 20 waiting in the shadows. In other words, you will never get rid of them all.

Slugs are slimy in order to survive. Being shell-less and made up mostly of water, slugs’ bodies are prone to desiccation; they generate protective mucus to survive. This is why they’re constantly surprising us under tarps, planters, big rocks, fallen logs: they like damp places. By the by, if you happen to get a little slug slime on your hands, just rub your dry hands together or on a dry cloth to roll the slime into a little ball, like rubber cement.

And they don't even care who's watching!

And they don’t even care who’s watching!

Slugs are hermaphrodites. Yup, for slugs it takes two, but it doesn’t matter who. Mating slugs encircle each other and exchange semen through their entwined genitalia (that’s the shiny blob you see in the photo). A few days later, each slug will lay at least 30 eggs in a dark, covered spot — like the nice, cozy soil in your garden beds.

And they can reproduce at any time of year.

Isn’t that just great?

(Upside: Sometimes they get stuck together, and have to chew off their own genitalia after mating. So there’s that.)

Slugs are generalists. As if you needed to be told. These things are like teenage boys on a growth spurt: They’ll eat almost any type of organic matter, consuming up to 40 times their weight every day.

So maybe slugs are not all bad? Since they do eat all kinds of organic matter, this will include decaying plant material, paper and cardboard, and even dead slugs, snails and other small soft carrion — all of which makes slugs part of the clean-up crew.

Plenty of anti-slug measures actually work! While it may prove impossible to completely eradicate slugs from your yard or garden, there are a number of ways to keep them out of your vegetable and ornamental beds.

  • Hand picking.
    Icky, yes — but also easy, cheap and green. Do it in the evening when slugs come out to feed. Drop your catch in a deep bucket of soapy water, stab them with a stick or scissors, or squash them underfoot. It really all depends on your level of squeamishness.
  • Copper bands keep slugs away from tasty leaves.

    Copper bands keep slugs away from tasty leaves.

  • Copper barriers.
    Copper rings, strips and mesh have proven effective in the Northwest. The feel of copper when it touches their slime gives slugs the willies. Try wrapping copper tape around circles of PVC and place around the bases of young plants, or add a border of copper mesh to the upper edge of raised beds.
  • Predator-friendly landscaping.
    Make sure your place is inviting to slug-eating birds, frogs, toads, snakes & beetles. Go easy on pesticides and noisy machinery, and provide shady, safe hiding places (like rock piles).
  • Debris cleanup.
    Reduce those dark, damp hideouts mentioned above; mow the grass and whack down those weeds.
  • Beer traps.
    Slugs are attracted to the ethylene, are overcome, and drown. (Since it’s the fermented sugar that draws them in, a mix of yeast, flour, sugar & water will also work.)
  • Chemical baits. Always follow label directions, use sparingly, and do not broadcast. All chemical baits, including ferrous (or iron) phosphate, can be dangerous to cats, dogs and birds. While the dangers of metaldehyde slug baits are pretty well documented, those containing iron phosphate were thought to be safe for pets but some recent studies suggest otherwise.

Also, where possible, try adding slug-resistant plants to your landscape. Landscape designer Carina Langstraat has a suggested list of slug-resistant plants for sun and shade that will work in Pacific Northwest gardens.

And for more info on dealing with slugs and other pests — including free .pdf fact sheets — visit the WSU Extension Online Store.

Image credits:
Slug head & tail, allaboutslugs.com
Slug mating photo, ©D.A. Salazar
Copper bands photo, allotment-garden.org


6 thoughts on “Everything You Always Wanted to Know About Slugs, But Were Afraid to — well, o.k., maybe you didn’t really want to know this much about slugs…

    • Copper definitely gets two thumbs up from me! It’s been the most successful anti-slug measure in my garden so far. I really recommend giving it a go. Also, it’s decorative, so win-win! :-)

  1. This is great Dolly. I knew some of these things, but had never thought about plants that are resistant to slugs. Good to know.

    • Thanks, Judy! I was pleasantly surprised to see the selection on Langstraat’s list — a better variety than I would have guessed. Maybe I should have grabbed some of those free day lilies at the spring sale after all…

  2. this article was so needed, thank you Dolly! i am a huge advocate for keeping ducks–it’s my favorite way to avoid slug problems, and they are a real joy to watch.

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