In the northern U.S., all earthworms are invasive.
According to the Smithsonian Environmental Research Center, native earthworms were wiped out more than 10,000 years ago by glaciers. That probably included the Driftless Area, which the last three glaciers have missed, because even though our topography was not chewed up and spit out the way the surrounding landscape was as glaciers ground over it and receded, conditions were pretty hostile to life when you are neighbors with a glacier.
The earthworms we see now started coming into the area with the European settlers in root balls or dry ballast from their ships.
I used to think they were our friends, but lately – not so much. Evidence is pouring in about the damage that earthworms can do to native environments like forests.
But that damage may be nothing compared to what is coming as an even more voracious earthworm is making its way into the Midwest and has been found in Wisconsin.
To learn more, check out my most recent article in Isthmus.
Worming Their Way into Wisconsin
When local gardeners turn over a spade of soil, they’re usually happy to find an earthworm or two. While these familiar worms were brought over by European settlers and are not beneficial to native habitat, they can form a healthy partnership with plants that farmers and gardeners have come to depend on.
Now these sometimes helpful critters risk being done in by their frenetic and destructive invasive Asian cousins, Amynthas spp., called jumping worms because of their hyperactivity.
The first Asian jumping worms sighted in Wisconsin were found in the UW-Arboretum in fall 2013 during a study session on invasive species co-hosted with the state Department of Natural Resources.
“One of the topics was a new Asian earthworm that we didn’t think had made it to Wisconsin yet,” says Arboretum ecologist Brad Herrick. “In a sugar maple stand behind our field shop, Bernie Williams from the DNR cleared away some of the leaf litter on the soil, and there were half a dozen of them snaking around.”
Since that time, Arboretum personnel have spotted the worms in other wooded areas. “We are monitoring their spread,” Herrick says. “They are from Japan, where they are found in grasslands. We are concerned about our prairies.”
Research on what these invasive worms do to the soil began in the 2014 growing season. By that October, Monica Turner, a UW-Madison zoology professor, and her graduate researcher Jiangxiao Qiu, discovered that the invaders dramatically change the surface layer of soil.
European and Asian earthworms are both destructive to native habitats. According to Herrick, “From what we’ve seen in northern forests, European earthworms in high numbers devour the leaves and organic matter, which limits germination and survival of native plants and in some instances allows other invasive plants such as buckthorn and garlic mustard to readily invade. We think Asian jumping worms will have similar effects, if not faster.”
When European earthworms burrow and feed, they leave behind castings that can improve the texture of agricultural soil and create slow-release fertilizer for plants.
Jumping worms follow a different pattern. They breed rapidly, relentlessly dropping cocoons. When the cocoons hatch, they grow to maturity in about 60 days, voraciously consuming all of the leaf litter and leaving harmful waste in its place.
“It’s happening really fast in the fall right now, when the worms are largest and at their biggest biomass,” says Turner. “They hatched in spring, and they have been growing all summer. They eat the leaf litter more rapidly and release nutrients much more quickly than European earthworms do. The jumping worms also leave behind elevated levels of phosphorus in the upper soils, which is already a problem for Madison lakes, and there is an especially large increase in nitrate. Nitrogen can be a useful fertilizer, but in the nitrate form it is very soluble and can pollute our groundwater.”
Read it all here.
Have you spotted these nasty fellows yet? Let us know.