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Invasive jumping worms creeping north through Minnesota

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The worms are coming.

Following hot on the heels of several more well-known invasive species, in the past few years scientists in Minnesota and Michigan have begun ringing the alarm bell about a new and potentially devastating invasive species. This new species has picked up a few names during its time in the spotlight, including the snake worm or 'crazy' worm, but you're most likely to encounter it under it's more common name: the Asian jumping worm.

And boy, what a worm it is.

Dr. Lee Frelich is an environmental researcher with the University of Minnesota Center for Forest Ecology who has been studying the worms and the effects they have been having on the ecology of the areas of Minnesota in which they have been spotted. Dr. Frelich noted that the Asian jumping worms have several things in common with their similarly invasive cousins, the European earthworms or 'nightcrawlers.'

“[The Asian jumping worm] is a whole group of species that are from Asia, from Japan, Korea, China, from that part of the world, so they're invasive,” Dr. Frelich explained.

“Of course, a lot of our earthworms are invasive here. The European earthworms have invaded decades ago in a lot of northern Minnesota, even remote parts of the Boundary Waters are infested with European earthworms, which are traditionally used as fishing bait, especially the nightcrawler. And that has major implications for the ecosystem in northern Minnesota because they cause leaching of nitrogen and calcium and so on out of the soil, even phosphorus into the water, and they can decimate native plant species that grow in forests.”

Yes, even our favourite little garden helper and fishing bait is an invasive species. All worm species that were native to Canada and much of North America were wiped out by the last glaciers, and the worms that hitched a ride over with settlers from the old world have since become ubiquitous to anyone who's taken a walk after a good rain.

But the jumping worms are different, and potentially more destructive. Dr. Frelich said that they are easy to identify on sight, partly because they are darker than the worms we're used to, but also through their alarming behaviour.

“They are distinctive, especially by late summer when they're mature,” he said.

“They thrash around with a snake-like motion that European worms don't; European worms are much slower moving than these jumping worms, and of course that's why they're called jumping worms. So you can tell. We're putting up a website that people should be able to look at that has some video clips and some pictures and it's meant for training for master gardeners who live throughout the state who we're hoping will give us information on the presence of these worms so we can see how widely they're distributed.”

The worms can also be distinguished by the clitellum, the raised and discoloured section on earthworms that make up part of their reproductive systems, which on the jumping worms is smooth and pale as opposed to the earthworm's raised and orange-y section.

The destructive nature of the worms also stems from another way they are different from more common earthworms. The jumping worms live on top of the soil and feed on leaf litter and organic materials there, rather than burrowing underground, and when the jumping worms process the organic matter into waste – known in the worm world as castings – it creates a big problem.

“They make the top two inches of the soil into little granules or pellets that are a lot like cat litter or coffee grounds, and they're not connected to each other,” Dr. Frelich said.

“They're just sitting there loose. So if they invade a forest that's on a steep hillside, if you step on it you just slide down the hill because the top couple inches of the soil is just laying there completely loose. So it could lead to a lot of erosion of soil and nutrients into the water, so that's the big concern.”

The loose soil also impacts plant life whose roots are unable to get a firm hold of the ground, leading to the entire plant being untethered from the ground.

While Dr. Frelich said there's still plenty of research going on into the worms, their biology and effective ways to stop them, he noted that there is one thing they know for certain: the worms are as far north in Minnesota as Duluth, and even our Canadian winters might not be enough to stop them.

“The jumping worms are basically an annual species. They hatch in the spring they become adults by late August or early September and then they lay millions of eggs,” he said.

“These worms are surviving here, so they can probably survive in northern Minnesota. The only limiting factor would be if the summer is long enough for them to mature. Summers are pretty cold in Duluth because they're right on Lake Superior, so if they're surviving in Duluth they can probably survive up near International Falls too.”

Even with adult worms dying each winter due to the cold, enough eggs are laid that by the next spring, the problem has only grown. Dr. Frelich confirmed research is ongoing into getting rid of the problem once the worms have arrived through the use of things like saponins, naturally occurring toxic compounds found in some plants, which are already used to control worm populations on some golf greens. But the best way to deal with them, he said, is to prevent them from arriving in the first place, which is easier said than done, considering how easy they are to spread.

“They can be moved around in mulch,” Dr. Frelich explained.

“So it's just a matter of someone going to Menards or whatever big box stores you've got there, and happen to get some mulch or someone who has a summer house up there brings some garden plants up there from Southern Minnesota to their summer cabin and happen to have the eggs or the worms of these jumping worms that they could be introduced there. That's definitely how they could get there.”

Dr. Frelich said people should carefully examine any mulch or plants to be sure they are worm free, and to clean off dirt from shoes, vehicles and other surfaces when travelling from areas where the worms live.

The Canadian Border Services Agency prohibits mulch or plant matter from crossing the border into Canada, so the risk is somewhat lessened that someone could bring a contaminated bag back home with them, But the eggs are small, and the worms are occasionally sold to anglers in some parts of the United States. All it might take is a few avid sportsmen crossing back home with the wrong clump of dirt trapped in the wrong spot, or a worm carelessly discarded on our side of the river, and we too could be facing down a jumping worm invasion.

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