I recently learned that all the native earthworms of Canada and the northern US were wiped out during the last glacial event, and any worms living in those forests now have been introduced from Europe or Asia. Is this actually a problem? Most know earthworms as a gardeners best friend, aerating the soil while spreading both nutrients and microscopic lifeforms. Unfortunately, these northern forests have spent the last 10,000 years evolving without earthworms, and so much of the local fauna has come to rely on leaf litter which the worms eat through.
Living in Virginia, we are below the Wisconsonian glacier line, and there are earthworms native to our area, including Lumbricidae Bimastos, L. Eisenoides, Lutodrilldae Lutodrilus, Megascolecidae Diplocardia, Ocnerodrilldae, and Sparganophilidae. The most common exotic earthworms north of Pennsylvania are the European species of Lumbricidae, also known as nightcrawlers. However, three species known as asian jumping worms – Amynthas agrestis, A. tokioensis and Metaphire hilgendorfi – have recently been gaining ground in the eastern US. Also known as crazy worms, they’re able to outcompete even other invasive species of earthworm.
Even though there are earthworms native to Virginia, the newcomers often operate in different niches, and their unique gut microbes cause changes to the soil chemistry. A study published March 30 of 2022 in Biology Letters looked at 60 plots in an aspen and poplar forest in Alberta, Canada, and found that as the number of earthworms increased, the diversity and abundance of aboveground invertebrates decreased. Another study found that the introduction of non-native earthworms can reduce plant diversity, and a pair of studies have shown negative impacts on salamanders and certain ground nesting birds.
So what can be done? Well, since there is no effective way to remove non-native worms from an area, all we can do for now is to limit the spread. Fortunately, worms spread only very slowly by themselves. The asian jumping worms mentioned earlier have been in the US for over a century, but have only recently begun spreading, helped along by humans who use them for fishing bait, and for compost. It also seems that older forests are more resistant to invasive earthworms, making yet another reason to preserve those forests that have never been logged.
So next time you go hiking, washing your boots and your tires can remove any worm eggs trying hitch a ride. And next time you go fishing, make sure any worms you brought for bait and any soils that might be carrying their eggs are not able to get out into the environment.
Sources:
https://academic.oup.com/bioscience/article/52/9/801/248749?login=false
https://www.sciencenews.org/article/invasive-jumping-worms-damage-soil-threaten-forests
https://ecosystemsontheedge.org/earthworm-invaders/
https://www.backyardecology.net/native-and-non-native-earthworms-in-the-eastern-u-s-with-mac-callaham/