Black Slugs Invade Whittier

By Marc Donadieu
Glacier City Gazette

The European black slug has established a foothold in Whittier.

The invasive species, first appearing 30 years ago in Cordova, is spreading.

The U.S. Forest Service has started studying the shiny, black, slow-moving slugs to determine their population density and what possible effects they may have on native plants and the wildlife that eat them.

Barbara Lydon is a Ranger in Nellie Juan College Fjord Wilderness Study Area, which covers over 2 million acres in Prince William. As a participant to the on-going study, Lydon is charged to collect and count black slugs before killing them.

The Gazette went into the field with Lydon to learn about the slugs, the study and to photograph the slimy creatures at close range. In pursuit of our prey, we set out for The Sportsman’s parking lot and The Manor, locations where the slugs are known to be abundant. Lydon said the temperature of the crisp morning was a few degrees above when the slugs hunker down, so the odds were good we would find some.

It wasn’t long before we found the first contestant, and it made quite the impression. The big black slug was chowing down on a dog turd, a behavior which some regard as a valuable community service. Feces are part of their diet as well as plants. A stick was used to separate the slug from its last meal before the sentence of death was pronounced. It was quickly dispatched with a thorough, squeaky squish from a boot.

Lydon explained the slugs’ typical diet and how it could potentially impact the local ecosystem.

“They prefer seedlings,” she said. “They eat vegetation, stems, fungi and moss. They could potentially have a negative impact on the ecosystem by changing plant diversity. Social and economic implications are two things to consider. They’re an eyesore. You look at them feeding on dog feces. It’s not pretty to look at.”

Lydon’s instruction to kill the slugs after finding them is part of a containment program to slow their spread and keep them confined. Eradication is not a current goal, but she encourages people to kill them when seen. If the slugs become well established, they are more difficult to control.

“They tend to be found in human populated areas and along roadsides,” Lydon said. “They’ve been in Cordova for over 30 years. They’re just starting to be reported and sighted in other places. We have confirmed sightings in Whittier, in Girdwood, in Chenega Bay, in Eshamy Bay and one of the hatcheries out in the sound has reported them.”

Implications of the invasive species presence are unknown, prompting further Forest Service study and increased public awareness of the slug as a mollusk non-native to Alaska.

“There hasn’t been a lot of research done on European black slugs,” Lydon said. “As we learn more about them, nothing has been confirmed. We’re trying to figure out why they’ve been in Cordova for 30 years and why they’re just starting to pop up in other areas.”

To gather data, Lydon and others set up transects or lined grids 100 meters long and 20 meters wide. Then the slugs within are collected, counted and later killed. Diverse areas are chosen to get population estimates and how far reaching they are. As elevation goes up, slug density goes down, which might be related to cooler temperature. The data is then analyzed to determine control measures.

Lydon described the slug disposal process used in remote areas of Prince William Sound. About 400 slugs were collected in two days and taken to the beach where they were salted and burned.

“What we’ve done out in the Sound is build a really, really hot fire in the tidal zone. We put these slugs on top, and it’s completely disgusting. You see that slime trail right there? They start to exude this slime, and they start sliding out of the fire. They don’t burn up and get crispy. They get kind of charred.”

The slugs’ slime is surprisingly strong stuff that is very difficult to remove.

“When we first collected these guys,” Lydon said, “we put them in a five-gallon bucket. It was incredible. They created a layer of slime like that, and you couldn’t get it off. I had gloves on, and you can’t scrape it off. I had simple green and scalding hot water trying to scrub off this stuff.”

If slugs are found, or if you’re out collecting them for disposal, the preferred method is to pick them up, salt them and burn them. Lydon also recommends squishing them, which is a faster method. She emphasized what not to do when killing slugs.

“What we don’t want people to do is throw them in saltwater or freshwater or put them in the garbage or dumpster,” Lydon said.

The City of Whittier is onboard with working alongside Forest Service to help with control measures and has issued a resolution.The Forest Service is also trying to initiate a spring program with Chugach School District.

“The teachers would like to be involved, and we’ve talked about going into the classrooms and talking to the school children and bringing them out here on field trips and doing what we’ve been doing with our other youth groups – setting up transects, getting an idea of the density of these populations and where they are at.”

“When invasive species are first discovered is the time to make a difference,” Lydon said.

If the affected areas are in the early stages of black slugs being reported, the Forest Service, field data in hand, can initiate control measures and make a difference to kill as many as they can.

“There’s a concern of introduction and expansion,” Lydon said. “What people should know is that they should be killing these slugs by either picking them up, salting and burning them or squishing them.”