Fading Forest Floors

Twirling cascades of yellow leaves cast Wolsfeld Woods Scientific and Natural Area near Long Lake in golden light. But instead of gazing up at the fall foliage, I scan the ground.

I’m looking for signs of jumping worms (Amynthas species), an invasive earthworm that has begun to transform the forest floor of Minnesota’s hardwood forests. Jumping worms don’t jump, but they do rapidly writhe about when disturbed. Dark in color, the worms feast their way through leaf litter, drastically altering soil structure and disrupting plant growth.

I kneel near a fallen log and start to shuffle through the soil, on the lookout for coffee ground–like castings—worm poop. I’m hoping to contribute some data to the University of Minnesota’s Jumping Worms Project, a citizen science effort to track the spread of jumping worms throughout the state.

The invasive worms are native to East Asia. It’s unclear how they initially arrived in North America, but humans have been helping them spread via mulch, fishing bait, and other sources. They’ve been observed in Minnesota since 2006.

Understanding the current extent of jumping worms in Minnesota is critical to preventing further spread. “We’re trying to find invading fronts—areas that mark the boundary between where jumping worms have and have not reached yet,” says Lee Frelich, a University of Minnesota forest ecology professor who is leading research related to the project. 

Most jumping worm reports have come from the Twin Cities area, and others from Rochester and southeastern Minnesota. Jumping worms have not yet been confirmed in the northern half of the state, which holds the majority of the state’s hardwood forests.

The worms feed on fresh organic material at the soil surface. “Usually, leaf litter accumulates in these forests over multiple years and decomposes slowly,” explains Frelich. But jumping worms speed up the decomposition process, leaving the soil exposed and vulnerable to erosion. The altered soil also makes it harder for native plants to root. 

It’s not too late to stop the spread of jumping worms in Minnesota. Laura Van Riper, terrestrial invasive species coordinator for the Minnesota Department of Natural Resources, stresses that preventive action begins close to home. She suggests brushing off shoes before and after hiking, using only heat-treated compost, and throwing all unwanted bait worms in the trash. “The idea that an ounce of prevention is worth a pound of cure is true with invasive species,” says Van Riper.  

I exit Wolsfeld Woods empty-handed. But before I leave, I scrape my shoes at a boot brush station. If I happened to pick up any jumping worm eggs, they won’t be coming with me.