Nonnative earthworms pose ‘serious threat’ to North American biodiversity

The researchers relied on data spanning from 1891 to 2021, including spatial distribution information and reports of nonnative earthworms intercepted by the U.S. Department of Agriculture. A machine learning analysis of species richness revealed that nonnative earthworms are probably the dominant species across 73 percent of the continent, with 28 percent of North America now devoid of its original earthworm species.

Overall, the researchers pinpointed 70 unique species of alien earthworm, the majority of which originate from Europe and Asia. The use of earthworms for fishing bait and the sale of vermicomposting materials are partly to blame, the researchers write, and the creatures tend to enter the continent from coasts and areas with airports.

The environmental changes wreaked by the new arrivals vary, from taking over areas with few native earthworms to spurring changes in the plant composition of forests and other areas.

Earthworms are often seen as positive forces in their native habitats, but the researchers point out that nonnative species can have the opposite effect. The invaders’ slow movements and feeding habits can cause soil compaction that precludes plant growth, reduce biodiversity, enable invasive plant takeovers and hurt trees such as the sugar maple.

“Because it is virtually impossible to remove established populations of alien earthworms,” the researchers write, “the best management option is to focus on prevention and early detection.” They call for policies to prevent the future spread of the alien earthworms, noting that climate change will probably drive future invasions.