Popular Slug-Killing Biopesticide Wipes Out Banana Slugs in Lab Tests

Where is the product sold?

The products already have a foothold in several countries, and efforts are underway to bring them to the U.S., Denver said.

• Original Nemaslug is sold in Kenya (as Slugtech), Canada (as NemaNights), and throughout Europe.
• Nemaslug 2.0 is available in England, Scotland, Wales, Austria, and Germany.

Why the banana slug matters

Ranging from Alaska to California, the Pacific banana slug is the world's second-largest terrestrial slug — smaller only than Europe's ash-black slug. It can reach nearly 10 inches (25 centimeters) in length. It's also famously the mascot for athletic teams at the University of California, Santa Cruz.

"It's a pretty iconic and charismatic species," Denver said, adding with a smile, "at least for a slug."

The current study builds on earlier research showing P. hermaphrodita is deadly to another native Northwest species, the Pacific sideband snail.

How worried should conservationists be?

Quite a bit, according to Taylor, who was an OSU graduate student during the study and is now a researcher at Oregon Health & Science University.

"This research has pretty big implications for biodiversity conservation," Taylor said. "The Northwest, due to its rainy climate, is a terrestrial gastropod hotspot" — meaning the region naturally hosts an unusually rich variety of land-dwelling slugs and snails.

The stakes are high in historical terms. Terrestrial slugs and snails account for more than one-third of all documented animal extinctions since the year 1500, Denver noted. Beyond rising global temperatures and habitat loss, "gastropods have historically suffered greatly from poorly designed and executed biocontrol attempts," he said.

The researchers point to a sobering precedent: one biocontrol effort involving a nonnative snail led to the extinction of hundreds of native snail species in Hawai'i and other Pacific islands.

What don't we know yet?

Plenty. The distribution of both nematode species in the Northwest remains undetermined, Denver said.

• A 2018 paper by some of the same collaborators reported P. hermaphrodita in Oregon for the first time.
• A 2024 paper reported P. californica in Washington state for the first time.
• Denver and co-author Rory McDonnell of the OSU College of Agricultural Sciences found P. californica in Oregon during a 2018–19 nematode survey.

The researchers — biologists and crop and soil scientists at OSU — note that biocontrol of pest snails and slugs has a checkered history, partly because unintended consequences for nontarget species remain understudied and hard to predict.

That's the study's core limitation, too. These were laboratory infectivity trials on slugs from one stretch of the Oregon coast, not field trials across the species' full range from Alaska to California. Still, with 100% mortality in one treatment group, the researchers say more research is needed before the products win U.S. approval.

The paper, by Emily R. Taylor and colleagues, appears in PLOS One (DOI: 10.1371/journal.pone.0361391).