The ecosystems of southern Michigan were worm-free until European settlers introduced them, along with the dandelions, queen-anne’s-lace, and a host of deadly diseases. I don’t know how prevalent earthworms worm before the last ice-age, but there were none left when the final glacier retreated 12 or so thousand years ago.
If you think earthworms are nothing but benign, you are misinformed. Yes, they help aerate heavy soils, but in light-to-medium textured soils they can be devastating by consuming the organic matter and decimating the productivity of surface horizons. In the sandy soil where I garden in Chelsea, incorporating compost only improves the soil for several seasons, after which the action of earthworms leaves it positively crumbly, sterile and hydrophobic — in fact worse than before I added the compost. I hate them.
There’s a new species of earthworm headed our way. It’s the “crazy worm.” Last year it was found in the University of Wisconsin’s arboretum. It’s called the crazy worm because it jumps around so wildly that it is not possible to hold in one’s hand. It comes from Asia and is so prolific and aggressive that it drives out our familiar “native” European earthworm. The worm reaches maturity in just two months, and is parthenogenic (no mate required). As a result populations explode rapidly. No good will come from it.
Our native plant communities evolved without earthworms. Quoting from the University of Wisconsin-Madison’s News: “‘Amynthas [the crazy worm] was listed as a prohibited species under Invasive Species Rule NR 40 since its adoption in 2009, because we knew their introduction into our state poses a huge threat to the future of our forests,’ says Bernie Williams, invasive species specialist in forest health at the Wisconsin Department of Natural Resources.” The worms eat so much that they eliminate the spongy surface organic layer and leave behind an easily-compacted, balled-up water-repellant granular soil.
Here’s a link to the article in the News: www.news.wisc.edu/22996.