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Slimed: Non-native Slugs in Alaska

by | September 7, 2022

It’s been raining, and you know what that means…slugs.

Most Alaskans are familiar with slugs, arguably one of nature’s most maligned and misunderstood creatures. Whether they’re skeletonizing your garden greens, devouring the mushrooms that pop up in your too-wet-to-mow lawn, or sliming around in the leaf litter along your favorite trail, Alaska hosts multitudes of slugs. Particularly the cooler, wetter parts of the state. And they seem to be everywhere this year.

But where do all the slugs come from?

Grey and brown-colored slug on green leaves with holes in them
Commonly found in Alaskan gardens, grey garden slugs (a.k.a. grey field slugs) are considered pests in much of the world. PC: Jen Chauvet/Homer SWCD

Slugs in Alaska

Some slugs are native to Alaska. The charismatic banana slugs (Ariolimax columbianus) of Southeast, for example. Others, like the leopard slug (Limax maximus) and grey garden slug (Deroceras reticulatum), were brought here from elsewhere. Probably on boats or tucked away in the soil of plants we buy at our local nursery. But no one really knows – it’s hard to track something as elusive as a slug or its minute eggs.

Large brown slug with black spots on a moss-covered log
Native to Europe, North Africa, and parts of Asia, leopard slugs have become invasive in parts of North America, South America, Australia, and New Zealand. PC: Frank Vassen, CC BY 2.0, via Wikimedia Commons

Grey garden slugs, the slug you’re probably most familiar with, have been in Alaska for as long as anyone can remember. They go wherever people go – what we might call a “cosmopolitan species” – and are likely not going anywhere (not very fast, anyway).

But there’s a new(ish) slug on the scene, and it’s not your average garden slug.

Enter, the European black slug (Arion ater).

A large black slug on a green leaf
Native to much of northern and central Europe, the large European black slugs are characterized by the deep grooves that run along their back. They thrive in cool, wet climates associated with coniferous forests. PC: Maura Schumacher/Kenai Watershed Forum

New Slugs on the Block

The first report of European black slugs in Alaska came from Cordova in the 1980s. From there, the slugs spread throughout Southeast, where they have become a serious pest. We’re talking hundreds upon hundreds of slugs, perhaps in a single backyard. From Ketchikan to Haines, agitated gardeners and non-gardeners alike lament the introduction of European black slugs.

And they continue to spread.

Don’t be fooled by the name – European black slugs can vary in color from dark black to orangish red, brown, tan, or even nearly whitish. They can also be confused with other Arion species. NPS photo

European black slugs of all colors and sizes have been confirmed in Southcentral, Kodiak Island, and as far west as King Salmon. A few reports have even come in from Adak.

Fortunately, outside of Southeast, European black slugs don’t seem to be securing a foothold. Except in Whittier, where a sizable population has cropped up in recent years. At the 2022 Whittier Slug-Out, volunteers removed over 500 of the invasive slugs from Smitty’s Cove, a popular access point for boaters and kayakers heading out on the Sound.

Two people wearing hats crouch by a white bucket. One person holds a large black slug in a plastic bag while another person shows a similar black slug in their gloved hand.
European black slugs have firmly established themselves in the Whittier area. During the 2022 Whittier Slug-Out – an event hosted by the Prince William Sound Stewardship Foundation, the Kenai Watershed Forum, and the U.S. Forest Service – volunteers learned about European black slugs, while plucking hundreds of them from the area near Smitty’s Cove. PC: Maura Schumacher/Kenai Watershed Forum

Why are European Black Slugs a Problem?

Worldwide, slugs represent one of the most troublesome pests of agriculture and gardens. And while most slug damage – slime trails that are a bear to scrub off and/or holes carved into leaves – is cosmetic, extensive damage can significantly stress or even kill plants.

But how does our experience with slugs in the human-built landscape of farm fields and raised beds translate to native ecosystems? Or, for that matter, to European black slugs in Alaska?

That’s the thing, we really don’t know. A risk assessment for the Copper River Delta published by the Alaska Natural Heritage Program in 2010 stresses the need for more research, citing high uncertainty about what European black slugs might mean for Alaska’s native species and ecosystems.

We still have so much to learn.

A large black slug in wet moss
Ravenous omnivores, European black slugs are efficient recyclers of waste. They’ll eat just about anything decomposable – plant matter, fungi, animal feces, and even other slugs. PC: JoelineLange, CC BY-SA 4.0, via Wikimedia Commons

Unraveling the Mystery: How You Can Help

First of all, if think you’ve seen a European black slug, report it! Visit the Univeristy of Alaska Fairbanks Cooperative Extension Service’s AK Pest Reporter to submit your sightings – your contributions help the scientific community better understand European black slugs in Alaska. While you’re at it, check out the new Alaska Slug and Snail Watch page to learn more about slugs in Alaska and peruse a cool slug map.

No doubt about it, European black slugs seem to have established themselves in parts of Alaska. But that doesn’t mean we have to sit back and watch them slowly settle in everywhere, like they have in Southeast. Documenting their whereabouts and considering their potential to cause damage, paired with precautionary actions – like inspecting boats, kayaks, and boots when recreating in areas known to harbor European black slugs – can prevent them from spreading further, ultimately protecting Alaska’s native ecosystems on the Kenai Peninsula and beyond.

And really, come rain or shine, isn’t that what it’s all about?

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