A global research team, including scholars from Stanford University in the United States and Sorbonne University in France, along with other institutions, warns that North America faces ecological stress from a growing number of invasive earthworm species. The findings were published in Nature Ecology and Evolution, a leading scientific journal focusing on ecological and evolutionary research.
Analyses indicate that North America hosts at least 70 species of invertebrates that establish themselves in new areas and disrupt local ecosystems. Researchers compiled thousands of records spanning 1891 to 2021 to build a comprehensive database of native and non-native worms. This was paired with a second dataset detailing detections of non-native worms along the U.S. border from 1945 to 1975 to enrich the historical perspective.
Results show invasive earthworms have colonized 97% of soils tested across the continent. Today, non-native invertebrates account for about 23% of the roughly 308 worm species found in North America. In contrast, nonnative statuses are much rarer among other animal groups: roughly 8% of fish, 6% of mammals, and 2% of insects and arthropods are introduced elsewhere in the United States.
In Canada, the share of alien worms is roughly three times higher than that of native species. Across much of the U.S. lower 48 states and Mexico, the ratio is close to one invader for every two native species.
In the northern broadleaf forests of the United States and Canada, the presence of non-native earthworms alters soil microhabitats and affects tree roots, including those of sugar maples. These soil changes reverberate through the food web and can promote the spread of invasive plants, complicating forest health and nutrient cycling.
Invasive worm species tend to gain an advantage because many females can reproduce without mating, enabling rapid population increases. Warming temperatures in northern regions also expand suitable habitat as permafrost thaws and native earthworms decline in those soils, creating new opportunities for non-native species to establish themselves.
Scientists caution that not every introduced worm poses a threat, but the prospect of a stealthy invasion raises concerns about losses in North American biodiversity and the potential disruption of native soil communities.
There is ongoing discussion about whether certain invasive organisms that appear less conspicuous could have disproportionate ecological impacts, underscoring the need for ongoing monitoring and management across borders to protect soil health and ecosystem services.
Notes from the study highlight cross-border data linking on both sides of the Canada–United States boundary and emphasize a coordinated approach to understanding and mitigating invasion risks. Evidence from the field and records kept over decades illustrate how human activities and climate trends intersect with natural processes to shape worm distributions across North America.