by Gabrielle L. Wheeler
Since grade school, we were taught that earthworms are important to the ecosystem: necessary for keeping the soil rich and indispensable to agriculture. This can be true, but as with most things, it is more complicated than that. As it turns out, earthworms are not native to North America and as such can and do have negative impacts on local flora and fauna. To some, they are considered an invasive species and a pest.
North America once had native earthworm populations but during the last ice age, some 10,000 years ago, they went extinct. The earthworms that we think of when we imagine farmers plowing fields are progeny of worms that have been brought via plane or boat beginning with the first European settlers. Major movements of humans around the globe since then have brought multiple species to inhabit our soils today.
Farmers and gardeners do love earthworms in their soils, especially endogeic species, because they eat through organic matter, including leaves and clippings, and their poop, or castings, act as fertilizers for the soil. All the while that they are chewing and pooping, they are also moving and burrowing. This aerates the soil and supports absorption of oxygen, water, and nutrients in plant roots. These are all helpful things for prosperous plant growth.
Or so it seems. As it turns out, some native North American forest ecosystems become negatively impacted by the presence of earthworms in woodland soils. According to an article on Cornell University’s New York Invasive Species Research Institute webpage by Annise Dobson, earthworms have a negative impact on some sensitive plant species such as trilliums. By quickly chewing through and digesting the uppermost layer of leaf litter, the forest floor may be left mostly bare. Plant species such as trilliums, and true and false Solomon’s seal depend on the layer of detritus and are negatively impacted by its absence. The non-native worms also appear to have negative impacts on some native forest fauna as well. Invertebrates that would normally inhabit the leaf litter may be absent, negatively impacting some fauna that depend on them as a food source. Salamanders that depend on the temperature regulation of leaf litter may also be negatively impacted.
Who would have guessed that the common, little earthworm could create such stir? It’s undeniable that earthworms support agriculture but how do we keep them out of our forests? Simple, don’t release them there and don’t move dirt. Earthworms don’t get around too fast without a helping hand.