Minnesota's 'jumping worm' invasion upends spring plant sales

In Anne Lippin's 25 years of gardening, she's never been so traumatized over a pest. "It's really demoralizing," she said, "to have an invader where I can't combat the invader."

To her great distress, Lippin received confirmation from the Minnesota DNR last summer that she had, indeed, found jumping worms in her St. Paul yard. "If you've been working on a painting for 25 years and you suddenly discover the canvas is rotting — that's what it feels like," said Lippin.

Also known as the "crazy worm," "Alabama jumper" and "snake worm," this wildly wiggly Asian earthworm (Amynthas spp.) that can cause soil erosion and ultimately kill plants is now reported in the Twin Cities, Rochester and possibly Duluth, as well as southeastern Minnesota and western Wisconsin.

The invasion is forcing many Minnesotans to rethink this spring's plant sales, plant swaps and green practices in general, affecting everyone from home gardeners to garden clubs to garden centers and mulch suppliers.

"It's pretty likely that they're distributed in virtually every neighborhood in the metro area," said Lee Frelich, one of the country's top forest ecologists at the University of Minnesota. Not that jumping worms are living in every square inch of soil, he explained, but "if they're in one place in a neighborhood this year, they're going to be all over the place next year."

All Pat Thompson could utter was a high-pitched "Ahhhh" when she heard the news that jumping worms have infested dozens of garden beds at the University of Minnesota, just two blocks from her house. "If [rain] water is moving the cocoons downhill from the St. Paul campus toward me, what can I do about that?" she said.

After examining the soil under ginkgo trees on campus last fall, Frelich discovered "you could just dip your hand in there and get a handful of worms."

The creatures are particularly hard to find in the springtime even for the most vigilant gardener. The "hatchling" worms are too small to identify yet, and their egg cocoons are tiny — like a mustard seed.

That means gardeners may unknowingly spread the worms by sharing plants through garden clubs and spring plant sales. By late July, the mature, 4- to 5-inch-long worms begin to cause noticeable damage, and are laying eggs that can overwinter.

"If you do have jumping worms, one of our first messages is 'keep calm,' " said Laura Van Riper, the DNR's Terrestrial Invasive Species Program coordinator.

What's the threat to gardeners? Experts say "massive" soil erosion is a primary concern, especially on slopes. The jumping worms rapidly eat leaf litter and even larger chip mulch, turning the top 2 inches of soil into a distinctive, coffee-ground-like texture. The loose layer of separate particles "just washes away in heavy rains," said Frelich.

"If you mulch with leaf litter and you have jumping worms, you're essentially feeding them, and their population will explode," said Frelich. The worms also absorb key plant nutrients.

When a garden dries out, the worms cluster around the roots of plants and eat fine roots that absorb moisture. "They damage the roots so badly that they kill a plant," said Frelich, or plants gradually decline. Shallow-rooted plants have a hard time staying rooted.

It's enough to dampen enthusiasm for long-awaited spring plant sales.

"It's just a terrible, terrible thing," said Thompson, who co-chairs the St. Anthony Park Garden Club plant sale in St. Paul. "We are just trying to figure out what to do."

"Prevention is the only known solution," said Angie Gupta, a University of Minnesota Extension educator; she published a long list of plant sale recommendations on the Extension website.

She says clubs can prevent jumping worms from spreading to other yards by not accepting "dig-up" plants or garden materials from infested gardens. Otherwise, gardeners should completely submerge plant roots in water to wash away the soil, any worms and cocoons. The plants can be repotted with sanitized, bagged potting soil from a reputable dealer. Gupta advised buying bare-root plants whenever possible.

Ultimately, it's a case of "buyer beware," said Gupta, who encourages gardeners to ask questions. If you purchase plants from a reputable seller like a nursery or garden center, "it's probably OK," she said.

"We don't have any documentation at this point of jumping worms in any of our member facilities — whether they be growers or garden centers," said James Calkins, research information director for the Minnesota Nursery and Landscape Association. Growers use a peat mix in containers, Calkins said, which "is not a good substrate for jumping worms."

The DNR and Extension are asking Minnesotans to report when they discover jumping worms, and to send in high-quality photos for identification. The worms are smooth, brown or gray with a light-colored ring that completely encircles their body, relatively close to the head. On a European nightcrawler, the raised, saddle-like ring is farther down. Jumping worms also act differently. "They flail about so wildly," said Van Riper.

"I went through stages of grief," Gupta said, when she discovered the jumping worms in her own yard in Rochester. She suspects they came with the mulch she hauled from the Olmsted County compost site.

"They'll smell the mulch and move towards it," Frelich said. "If the worms get into a community mulch pile, they can spread from there to hundreds of individual gardens." Even commercially bagged, heat-treated mulch is suspect, Frelich said, because the bags can have holes and be recontaminated when stored outside.

For the next few summers, Frelich and his research team will study jumping worms' behavior and ways to control them at the Minnesota Landscape Arboretum, where over half of the woodlands are infested.

They're testing elemental sulfur, diatomaceous earth, slug bait and a natural chemical of black tea leaves called saponins, which is commonly used on golf course putting greens to manage earthworms. Frelich also is experimenting with heat and cold. "We know that 110 to 115 degrees is going to kill even the eggs," he said. That's why you're more likely to find the worms in a shady garden bed, rather than a hot, dry lawn.

Until he has answers, Frelich advises gardeners to be "really careful with plant sales, with mulch and to be really observant."

The frustration is acute for gardeners with jumping-worm-infested yards. "I was like, 'Fine, I am going to dig up my entire yard,' " Lippin said with a laugh. "I will dig it up foot by foot and remove every single worm that I find. And then I thought, 'Well, that's not rational.' "

Gail Brown Hudson is a Minneapolis freelance writer with a master's degree in horticulture from the University of Minnesota. She is an Emmy award-winning journalist, writer and video producer, as well as an avid gardener.