Earthworm Invasion: Warm, Wet December Brings Out Not-So-Goodguys

Earthworm Invasion: Warm, Wet December Brings Out Not-So-Goodguys

  • This article was written by Valerie Blaine, nature programs manager for the Forest Preserve District of Kane County. You can reach her at
Screen Shot 2015-12-15 at 8.56.04 AM

CREDIT: Valerie Blaine

In mid-December, we wouldn’t be surprised to find snow on our driveways. But earthworms? In December? That’s just what I found on the driveway this morning.

This mild, wet weather has brought lots of earthworms out of the ground. The parking lot at Creek Bend Nature Center is practically crawling with night crawlers!

Is this a good thing or a bad thing? It depends on how you look at it. As the climate warms and average temperatures increase, lots of things get out of whack. Invertebrate animals — like earthworms — may become active in winter warm spells. In many cases, their predators have left for their wintering grounds. Predators and prey being around at the same time is a big deal, ecologically speaking.

There’s another problem with lots of earthworms, particularly night crawlers. Most earthworms in northern Illinois are invasive species — and night crawlers are notorious invaders. A recent study found that 20 of 38 species of earthworms in Illinois are not native. The forests of the upper Midwest evolved without earthworms since the retreat of the last glaciers. There is a different group of terrestrial decomposers here, and these leave a thicker layer of leaves (called leaf litter) on the ground. This thick cover of leaves is necessary for many species of plants. In turn, those plants are needed for native wildlife.

One of the biggest problems with invasive earthworms it that they are too good at what they do. They are great at digesting leaf litter, to the point of denuding the forest floor. The problem is so severe in Michigan that there is a “Great Lakes Worm Watch” program, training citizen scientists to monitor the invasive earthworms in the state. The goal of gathering this information is to help land managers find strategies to deal with the problem.

Yes, I know this goes against all that we were taught in grade school about earthworms being the “good guys.” It’s hard to wrap your head around the fact that these critters are not the heroes we thought them to be. Their reputation is forever soiled.

How did these not-so-good guys get here? As with many invasive species, some came accidentally. Whether in the soil of potted plants from Europe, Africa, or Asia – or in ship’s ballast, they hitched rides across the ocean. They move from state to state as fishing bait, dumped unused in the woods or fields. Some move around in clumps of soil on cars and trucks.

Removing invasive species from ecosystems is not easy. In the case of earthworms, it may be close to impossible. The key is to prevent their spread. Two ways to help contain these problematic creatures are better bait disposal and “equipment hygiene” (think: muddy tractor tires). Be cognizant of your compost pile — if there are large worms in it, don’t move it around. Spread the word about worms, but don’t spread the worms!

The silvery worm tracks left on the driveway today will likely be gone by Christmas. Replaced, perhaps, by tracks of native wildlife in the snow.

Upcoming Nature Programs

To learn about winter wildlife, come along on a naturalist-guided program in the Kane County Forest Preserves! We’ll explore Burnidge Forest Preserve in Elgin from 10 – 11:30 a.m. Wednesday, Dec. 30. From 1 – 2:30 p.m. Monday, Jan. 18, we’ll look for wildlife Hannaford Woods Forest Preserve in Sugar Grove. If you’re fascinated by owls, check out “Owls of the Winter Woods” from 7 – 8:30 p.m. Tuesday, Dec. 29, at Binnie Forest Preserve in West Dundee. The programs are free, and open to all ages. Advance registration is required. Call 630-444-3190 or email