Invasive earthworms of North America
[2] They are considered keystone species in their native habitats of Asia and Europe because, as detritivores, they alter many different variables of their ecosystem.
These earthworms increase the cycling and leaching of nutrients by breaking up decaying organic matter and spreading it into the soil.
[5] This change in the plant diversity in turn affects other organisms and often leads to increased invasions of other exotic species as well as overall forest decline.
[5][8] Among these, Lumbricus terrestris, L. rubellus, L. friendi, Amynthas agrestis, and Dendrobaena octaedra have been studied for their ability to invade previously uninhabited locations and disturb the local ecosystems and nutrient cycles.
[9] When organisms die and plants undergo senescence, their detritus fall to the forest floor, where they begin decomposing into their constituent nutrients.
Most northern forests in North America lack native earthworms, which were largely wiped out when the ice sheets of the Wisconsin glaciation scoured much of the continent down to the bedrock.
[12][13] Invasive earthworms have caused a decrease in diversity, seedling populations, forest floor organic matter volume, and overall habitat quality.
[1] Thus, few saplings or under-canopy plants grow to full maturity and generally only the larger trees with extensive root systems survive.
[14] Specifically, trees like poplar, birch, and maple are disfavored by the change in habitat, as are many forest herbs like Aralia, Viola, and Botrychium.
[15] When a decrease in overall ground cover and canopy vegetation occurs, the few plants remaining are often eaten shortly after germination.
[5] Generally, with the addition of earthworms to a forest, a decrease in diversity is observed, and often other exotic species follow that can survive the nutrient-diminished environment better than the natives.
[16] For example, in newly invaded forests buckthorn and garlic mustard, both invasive species, increase notably in population density.
[17] Moreover, the decrease in plant biomass due to species richness affects earthworms is directly related to trophic levels.
The worms were originally transferred through the horticultural trade, probably in the soil bulbs of European plants carried to the Americas.
[22] Evidence shows that Asian earthworms grow more rapidly,[26] reproduce more quickly, and have greater flexibility in their diet than European species.
The Minnesota Department of Natural Resources, in cooperation with local groups, has launched a public education campaign using posters in bait shops and other outreach efforts.
