Earthworms helpful in suburbs, but threat to woodlands

Let’s see…what’s the best way to put this…? 

I’ve got worms. 

Now, before you recoil in horror, let me hasten to point out that I’ve had them before. And, no doubt, you have too.   

Of course the worms we’re talking about here are earthworms. We all have them in our lawns and gardens and, thanks to recent bouts of rain, on our driveways and sidewalks too. Although it has seemed like there’s not quite as many as in years past (which, you’ll soon see, isn’t such a bad thing) we’ve still managed to pick up enough worms in the past week to resurrect the Hickory Knolls Worm Farm, a.k.a. the crisper drawer in the appliance we call the Animal Fridge. 

It’s true, fresh-picked earthworms make a wonderful addition to the diets of the Hickory Knolls education animals, particularly our turtles, salamanders and garter snake. They make great fish bait too. And everyone knows how helpful worms are in the garden, enriching and aerating the soil the way they do. 

But those same qualities that have made earthworms seem like such friends to animal keepers, fishermen and growers everywhere have caused the worms to become mortal enemies of our native woodlands.  

Familiar as they are, virtually all earthworms we encounter here in northern Illinois are aliens—exotic species from Europe and Asia. Although nightcrawlers—those hefty worms mostly nocturnal in nature—were brought here specifically for use as fish bait, the remaining species we have all came as stowaways in pots, planters and other sources of soil from “the Old Country.” 

Though relatively harmless in our suburban landscape, where lawn grasses and ornamental shrubs are largely nonnative, these foreigners spell trouble for our local woodland ecosystems.  Oaks, hickories and other native tree species, as well as many of our woodland wildflowers, require an environment where leaf litter and assorted natural debris break down slowly. This detritus, known as duff, in turn provides habitat for countless arthropods, fungi and other species that complete the complex matrix of a healthy food web. 

When earthworms move in, they quickly consume the duff. Nutrients that would have been available disappear, and the soil, rather than becoming aerated and loose, instead becomes harder and more compact, and leads to a loss of species diversity. 

In fact, scientists studying the health of woodland ecosystems are now finding that the presence of earthworms seems to go hand-in-hand with other exotic invaders that form monocultures wherever they land: European buckthorn. Asian honeysuckle. Garlic mustard. 

These associations, when you think about it, make total sense. The organisms co-existed together in Europe and Asia, so why not reunite here in the New Country too? 

The problem is so severe that a monitoring program, the Great Lakes Worm Watch, has been organized to keep an eye on earthworms and slow their progress. 

Founded by Cindy Hale, Ph. D., Environmental Education and Ecology professor at the University of Minnesota Duluth, the organization seeks to monitor the spread and measure the impacts of exotic earthworms in our region. Besides getting the word out about earthworms and their effects, the group also has developed an easy-to-use guide to earthworm anatomy, as well as a dichotomous key to help people identify some of the more common types of worms. 

One of my favorite GLWW activities—and one you can try at home—is to conduct an earthworm survey. Roll over logs to see what species live underneath. Dig a hole and sift through the soil to see what sorts of worms you’ve unearthed. Count nightcrawler middens—that is, the piles of cast material, or poop–these large worms leave behind. 

You can also create a mixture of water (4 liters, or about 1 gallon) and dry mustard powder (40 grams, or about 1/3 cup) and pour it over a 1-ft.x1-ft. section of soil. The mustard will act as an irritant and drive worms up to the surface where you can count them with ease. 

Because surveys aren’t much good if the findings go unreported, make sure you report your data to the folks at GLWW. Complete survey protocols can be found on their web site. 

Have you got worms? You know you do. Learn all about them at 


Pam Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or