I've always considered earthworms to be a good thing to have if they're working the soil. But apparently, some worms are doing more harm than good in certain situations. And once they've infiltrated an area, they can't be removed.
Bruce Snyder is an assistant ecology professor at Georgia College and State University and an earthworm researcher. He says there are over 170-species of earthworms in the U.S., and one-third of them were introduced from other continents. Some of these non-natives are very common.
"Nightcrawlers are a European species. Most of the ones that are sold for bait in most places of the country are non-native. Red wigglers, or the species that's usually called red wigglers, are also a European species," says Snyder. "But they're marketed under so many different names that it's hard to tell. Sometimes you go and purchase bait, and you actually get multiple species in the bait container."
Invasive worm species are only problematic in certain ecosystems. For example, northern forests evolved without earthworms due to glacial activity. But Snyder says since their introduction, earthworms have been eating leaf litter on the forest floor.
"The plants that live there need that leaf litter in order to regenerate. There are probably about five species that invade that environment. I did some of my research in the Great Smoky Mountains, and there are some Asian species which are actually invading there," he says. "We’re not seeing the same sort of impact, but I also study millipedes, and we found that those invasive earthworms are affecting the millipedes that live in the soil. So, depending on what ecosystem you're in, there can be different effects."
Snyder says if you put nightcrawlers in your garden, they probably won't create any problems. However, if you dump them in the forest after a day of fishing, there is the chance that they could disperse. He recommends tossing them in the water instead.