A subversive invasion is underway, and it is happening right below your feet. The keep has long-since been breached, the war already lost. Despite the best efforts of our native predatory birds, ants and mice, trespasser populations remain strong.

I speak, of course, of the exotic earthworm. That squirmy slinker masquerading under the guise of healer of the soil. Indeed, my dear shocked readers, Minnesota lays no claim to native earthworm species. The ancestors of any worm you encounter (sightings are rare because of their stealthy nature) hail from the soils of Europe or Asia. In fact, there are no native earthworm species in the entire Great Lakes region.

We have all been fed the earthworms’ propaganda: by ‘aerating’ and ‘mixing’ the soil, earthworms help to distribute nutrients and create fertile humus (note the intentionally vague terminology). Earthworm effects on soil structure and plant, animal and fungal community composition is far more complicated and controversial than they would like to have

you believe. Research conducted by the University of Minnesota suggests that the introduction of exotic earthworms have had cascading consequences for the ecology of native hardwood forests. These include the decimation of understory plant species and tree seedlings, and branching trophic effects on mammal, bird, and amphibian populations.

Earthworms are able to remold the environment so extensively as to facilitate the invasion of other nonnatives including buckthorn and the European slug.

What does this all mean for restoration efforts in the Arb? Little research has been done to investigate the effect of earthworms on prairie landscapes. Carleton students and professors are on the case! A healthy dose of concentrated mustard solution poured on the ground irritates the worms and brings them writhing to the surface, thus facilitating counting and identification. This week, the Population Ecology Laboratory fought back (results of the study yet to be determined)!

As a layperson, it is easy to feel helpless. What can one person do against such a pervasive adversary? I would not recommend watering your lawn with mustard, but you can check out “Great Lakes Worm Watch” to learn about opportunities for engagement as a citizen scientist.