The earthworm has finally soiled its reputation. That wiggly, useful invertebrate is wrecking havoc on forests around the country and causing scientists to label the once benign creatures as “voracious” and “destructive.”

Liam Heneghan, an associate professor of environmental science at DePaul University, has been studying botanical invaders in Chicago-area woodlands for quite some time. He said that until recently, the invasion of ecosystems by foreign earthworms was a very small area of scientific research. Most people are unaware that all of the earthworms in the Midwest are non-native European and Asian species. “We’ve been accustomed to considering them the ‘good guys’ because they increase fertility and aerate the soil,” Heneghan explained. “Then they became linked to the disappearance of rare plant species, and the picture changed.”

Heneghan was one of a dozen international scientists who convened at a meeting in Georgia recently to discuss the problem and possible solutions. He said that he came away from the meeting with the impression that the work being done in Illinois to preserve and restore diminished native plant species will assist in leading the way for a counterattack on the earthworms, particularly in urban areas where the problem of invasive species is more prevalent.

Heneghan and a group of environmental science students from DePaul have been conducting research on the impacts of invaders on native tree diversity in the Chicago Botanical Garden preserves for the past five years. When Heneghan and his colleague James Steffen at the botanical garden zeroed in on the destructive potential of the earthworms, they began to focus their research attention on the worms as well. “We’ve been studying the feeding habits of earthworms and conducted a project to determine if the worms are attracted to the leaf litter of particular plants,” Heneghan said. “We’ve also quantified the impact of the worms on the litter layers of the woodlands and have been staggered by the enormous impacts.”

Although the introduction of these creatures can be traced to a number of factors, including the discarding of fishing bait, the explosion of earthworms around Chicago may be directly related to the creatures’ preference for leaf litter from a certain species of shrub, European buckthorn, an aggressive invader species. The earthworm problem is worse around the Chicago area because there is a large buckthorn population in this region. While buckthorn litter is extremely attractive to earthworms, leaf litter from native species of plants, such as the red and white oak, is not nearly as appetizing to the worms.

According to Heneghan, one solution to the earthworm problem lies in continuing to manage and grow native tree species that earthworms don’t find appealing. “A lot of resources are going into both the preservation and the restoration of the oak woodland sites,” explained Heneghan. “Endorsement of our current management practices is going to be the best solution because it discourages invader plants that the earthworms have a taste for.”

Buckthorn shrubs and earthworms appear to reinforce one another. Where worms are prevalent, they create conditions that assist with the proliferation of buckthorn. Buckthorn, itself, is associated with unusually high soil fertility, a condition that the worms appear to love.

“If it wasn’t for the tragic circumstances of our degraded woodlands around Chicago, this would seem very cool, two unrelated species that can facilitate each other so effectively,” said Heneghan. “However, the mutual support between buckthorn and earthworms may be the Achilles heel for both species. Removing buckthorn should reduce earthworm numbers, and restoring oak species, which has unappealing leaf litter, should see that the numbers are maintained at low levels.”

The solution, Heneghan warns, is not as simple as it sounds. For one thing, getting rid of earthworms will not solve the problem because they are still very useful creatures in smaller numbers. Secondly, according to Heneghan, funding for research in this area is not readily available. “Fortunately, there is strong understanding and support in the region for land managers working to preserve endangered habitat in Chicago,” said Heneghan. “We’ve been fortunate at DePaul to get support for this work from the Gutsgell Family Foundation, which has aided student involvement in the project.”

Meanwhile, the leaf litter disappears so rapidly around the buckthorn trees until Heneghan believes it will eventually have a negative impact on small mammals and bird species that are supported by the litter layer. He indicated that this potential problem heightens the need to remedy the imbalance.

“Earthworms are just one more twist in a battle to restore natural resources,” said Heneghan. “I’m not sure we will ever get rid of the earthworm problem. However, if we continue to manage and monitor our woodland systems, we will mitigate it.”