‘Second-Wave Worm Invasion’

Third municipal compost site closes

In the wake of discoveries of a nonnative worm that’s believed to harm trees and gardens and transform soil composition, a third town has ordered residents to no longer pick up mulch or soil from a municipal compost site.

On the heels of restrictions in Egg Harbor and Sturgeon Bay this summer, the Town of Baileys Harbor’s Green Site stopped allowing residents to drop off brush, yard waste, old mulch or soil. The Baileys Harbor and Egg Harbor sites continue to allow household recycling such as bottles and cans, so those recycling portions of the sites remain open on scheduled days.

“Nobody can take any material at all from the facility. That’s including the dirt and the wood chips that are there,” said Ryan Weisgerber, Baileys Harbor public works manager.

Weisgerber said he is waiting for further instructions from the Wisconsin Department of Natural Resources (DNR) regarding restrictions to add or continue at the Baileys Harbor Green Site.

Samantha Koyen, Door County Invasive Species Team (DCIST) coordinator for the Door County Soil and Water Conservation Department, said that as of Aug. 4, Washington Island had the county’s only municipally operated compost facility without Asian jumping worms.

“Washington Island is basically for discarded fish guts and wood chips to help increase the carbon in the mix. It’s nasty,” Koyen said of the mixture, but the town’s mixture doesn’t appear to contain or attract jumping worms.

Koyen and DCIST, as well as Sturgeon Bay’s public works department, are asking people to report whether they have taken mulch or soil from the municipal sites, where they put it and an estimate of the date of that pickup. To reach DCIST, call 920.746.5956.

Precautions to Take

Although much is still being learned about jumping worms, researchers do know that they break down leaf litter and change the soil composition via the dry, gritty, coffee-ground–texture castings they leave behind. 

In Asia, trees and plants have adapted for eons to the muscular, wriggling worms. That’s not the case in the U.S., where trees and forest plants are still adapting to, or coexisting with, the “common” earthworms, including night crawlers, which are not native to northeastern Wisconsin, said Lee Frelich, a Northern Door property owner and a research associate in the Department of Forest Resources at the University of Minnesota.

The European worms arrived in the United States in the late 1800s or earlier, brought by people or companies introducing most of our popular nonnative garden flowers and plants, Frelich said.

“We call the jumping worm the second wave of the worm invasion,” he said.

Generally, the jumping worm has spread most rapidly in cities and communities as people trade plants or bring in mulch or soil to gardens, and then the worm moves to neighboring locations, Frelich said. But unlike some nonnative plants that DCIST can poison or physically remove, Koyen said there’s no “silver bullet” such as a chemical or “wormicide” to kill or contain jumping worms. 

There are, however, a few clear precautions that both Koyen and Frelich said people can take:

• Avoid moving leaves, mulch, clippings, brush trimmings and dirt off a property or to other locations. In addition to possibly transporting live worms from an infested spot to another, the Asian jumping worms’ tiny cocoons can catch a ride on shoes and car and truck tires in the process.

• Clean your shoes. If you have a property with invasive jumping worms, clean your shoe treads after leaving your property, and clean them before entering parks, hiking trails and natural areas.

• Buy bagged mulch. Most large suppliers of mulch are required to heat-treat mulch prior to bagging it, and bagged mulch often reaches a heat that’s too high for worms and even cocoons to survive when stored in the sun, according to Koyen and Frelich. Researchers advise people to leave newly purchased bags in the sun for several days so they can heat up to 105 degrees, which is believed to kill the worms and their cocoons.

• Let autumn leaves lie. Frelich advised people to allow leaves to stay naturally where they fall, especially in the woods around the perimeters of their lawns. Not moving materials around or off a property can slow the spread of worms. Plus, allowing leaves to stay put holds down soil temperature and gives trees and wildflowers the nutrients and habitat they would have naturally in northeastern Wisconsin.

• Don’t use jumping worms as bait. Koyen said they’ll get away or can wash up or be dropped on the ground, starting new infestations near lakes and waterways.

Hitchhiking Is Not the Only Way for the Jumping Worm to Travel

Very few studies have been completed on Asian jumping worms, but an informal experiment showed that the adults can spread without gaining a ride in potted plants or in mulch and soil transported from place to place, according to Lee Frelich, a Northern Door property owner and a research associate in the Department of Forest Resources at the University of Minnesota.

Frelich said that University of Minnesota employees dumped a pile of clean mulch in the middle of a parking lot, and within a few days, invasive jumping worms had apparently sensed the attractive habitat, traveled more than 100 feet across the pavement, and heavily infested the pile.