Citizen science project tracks slugs as they slither north

A long, thin black slug moves across the ground.
Photo by Hubert Szczygieł via iNaturalist
A meadow slug, Deroceras laeve, crosses the ground in Fairbanks on June 19, 2021.

It’s never fun to walk into your garden on a sunny Fairbanks summer day only to find cutworms have sliced your broccoli off at soil level, voles have left tiny tooth marks in your carrots or, worst of all, a moose has chomped on what was a giant cabbage. 

These are common garden invaders in Interior Alaska, but, in the past decade, a pest that frequently eats its way through salad greens and other plants in Southcentral and Southeast Alaska has also made its appearance in gardens north of the Alaska Range: slugs.

Their appearance has gone mostly unnoticed, and Tamara Bell, who teaches the Fairbanks Master Gardener class, notes that her students report that slugs haven’t been an issue for them. But we know slugs are here, in part because we now have a tool to track them.

In 2022, Joey Slowik, an integrated pest management technician with the University of Alaska Fairbanks Cooperative Extension Service, realized that little was known about the species and ranges of slugs in Alaska. That made it hard to track native, nonnative and invasive slugs. Working with the Alaska Invasive Species Partnership, he created a webpage where Alaskans could report slugs and snails.

So far, 12 slug species have been identified in Alaska, Slowik said. Two common species are the meadow slug, which is a small black slug related to the common gray garden slug, and a group of slugs called the tail-droppers. Banana slugs also thrive in Southeast Alaska’s temperate rainforest. More slugs have been documented, but it’s uncertain whether most are native or imported, he said. 

“It’s pretty difficult to say what was here because there was never an initial slug survey,” he said. 

In 2023, thanks to the citizen reporting tool, two invasive snail species also were identified in Kodiak. The two species have probably become established. 

Visit the UAF Troth Yeddha’ campus from 4-7 p.m. on Thursday, May 16, to learn more about citizen science and research conducted by scientists at the University of Alaska Fairbanks during its annual Arctic Research Open House. 

Slugs play an important role in the ecosystem. Classified as shell-less terrestrial gastropod mollusks, they’re efficient waste recyclers and eat just about anything that’s decomposable, such as plants, fungi and feces, Slowik said. They’re also cannibalistic. From a grower or consumer perspective, slugs’ largest impact is on leafy greens and other vegetables.

Most common slugs aren’t considered pests, unless they’re eating the lettuce in your garden or you’re growing leafy greens to sell. Meadow slugs generally live in yards or fields and are attracted to the damp earth and succulent plants in gardens. Tail-dropper slugs, so named because they can drop their tails like lizards when threatened, are attracted to fungi, and are encountered by mushroom growers and harvesters, for example.

Other slugs are more problematic. An invasive slug — the black arion, also formerly known as the European black slug — is rapidly spreading along much of Alaska’s coastline, from Southeast to the tip of the Aleutians. 

The black arion is a large slug — up to 7 inches long — that can range in color from black to orange-brown to red. They were first introduced in Cordova about 40 years ago and didn’t move around much, Slowik said. Then in 2000, they started showing up in Juneau and Ketchikan and have since migrated to nearly every island in Southeast. Now, they’re being reported in Girdwood, Anchorage, King Salmon, and as far west as Unalaska and Adak. There’s even a population on Midun, an uninhabited island in the Alaska Maritime National Wildlife Refuge. 

“That’s not too surprising,” Slowik said. “That’s a perfect climate for them.”

Where people go, slugs follow. 

“The transport vector is clearly us,” he said. “Midun is an island out in the middle of nowhere. It’s not getting floods, and slugs don’t tolerate salty water, so they’re not hopping on a log and riding in the ocean over there.”

On land, slugs are slowly expanding their range. Slowik said gray garden slugs have only been reported in the Salcha and Fairbanks areas in the past 10 years, although they may have been there longer. That’s just when people started to notice. 

“That one has been moving north,” he said. “It’s been a well-established slug in Southcentral since the ’50s, or at least that we have documentation of it. So it’s surprising that it’s taken this long to move that far north.”

The reason? Slowik said it could be a sign of a changing climate or changing agricultural practices that are allowing that slug to live north of the Alaska Range. Also, our homes and gardens are interspersed with a lot of wild land, which is where most slugs live. 

“So if a gray garden slug gets established in a lawn or a garden, they’re going to migrate out into the forest around them and eventually through the forest,” he said. “They don’t migrate fast on their own legs — the estimate is a slug will go about six feet a day.” 

If a neighbor reports slugs and your garden is still slug-free, Slowik said the best way to keep it that way is to hit them with their No. 1 limitation: moisture. For instance, he rototills a 2- to 3-foot buffer around his potato field, which keeps the vegetation down and acts as a dry moat. If it rains a lot, that buffer may be less effective, but it still works.

When designing your garden, keep moisture in mind. Raised garden beds made of wood are ideal habitats for slugs, who will dig into the moist soil to ride out the heat of the day. Likewise, walkways made out of boards essentially create slug hotels, places for them to reside when they’re looking for protection and moisture.

Less slug-friendly options include beds made of plastic or metal, for instance, and walkways made of gravel. 

If you find slugs in your garden or lawn, especially north of the Alaska Range, report them to AkPestreporter or iNaturalist. Also, if you see black slugs or any slug or snail that you don’t recognize, report them. 

If you want to eliminate slugs in your garden, you can put some beer in a cup (slugs are attracted to the yeasty smell) and set it in the garden so that slugs will fall in and drown. Commercial baits are also available. 

Knowing about slugs can also help keep them at bay. Slowik said he started to get reports of huge, bright orange slugs in the Rabbit Creek neighborhood in Anchorage. He investigated and discovered they were orange-colored black arion slugs. 

“Black slugs have the bad behavior of being attracted to fecal matter,” he said. “So if there’s a dog park, that’s where they go. And they’re cannibalistic. So if you smash a black slug, a bunch of slugs will migrate out to feed on it.”

People were finding these slugs in areas littered with dog poop and smashing them, he said. 

“It’s the perfect breeding ground for all of these slugs,” Slowik said. “It’s like a feedback loop of keeping the environment alive. It’s so obvious because we’re giving it what it loves.”


Learn about slugs

If you want to learn more about slugs, the UAF Cooperative Extension Service has a free,  self-paced online invasive slug course. It covers the biology, impact, and management of slugs as well as tools for reporting invasive slugs in Alaska.

The full course catalog includes several classes on invasive plants and forest pests. All course material can be viewed for free by clicking “view course content for free” beneath the description. No registration is needed. Participants can also complete the course and pay a fee to receive continuing education credits.

EDITORS: More photos are available online.