Despite their familiarity, earthworms are an invasive species in America's northern temperate forests. They arrived in the mid-1800s, with the arrival of European settlers. And today, humans continue to spread earthworms through activities such as road building, mountain biking, and bait fishing.
The notion that earthworms are damaging forests may be counter-intuitive—they are known to mix and aerate soil. However, those positive effects are specific to garden and agricultural soils. In forests, these tiny creatures are creating big problems.
Feeding and burrowing by earthworms compacts forest soils, leading to a decline in native understory plants and animals.
Cary Institute ecologist Peter Groffman explains...
When earthworms would colonize these sites, the forest floor would disappear. In about 3-5 years, the forest floor could be completely eliminated. And this created quite a bit of concern because there's a lot of data that show that the forest floor is very important in these forests. It protects the soil from erosion. It's where most of the roots live. And there's a whole suite of biodiversity that lives in the forest floor: spring ephemeral plants, salamanders, and other soil organisms, and they are all greatly disrupted when the earthworms remove the forest floor."
There are no known methods for removing invasive earthworms. But you can prevent their spread by responsibly disposing of fishing bait and taking care not to transport leaves, mulch, or soil that may contain earthworms.
Be aware that common compost worms are invasive. Be sure to compost in containers and freeze compost before moving it into your yard to kill worms and their eggs.
Produced in collaboration with WAMC Northeast Public Radio, this podcast originally aired on December 27, 2013. To access a full archive of Earth Wise podcasts, visit: www.earthwiseradio.org.