An Invasive Species?
Earthworms are so ubiquitous here in North America that we take them for granted. But chances are that if you live in the US or Canada, many of the earthworms you see are not native species.
According to Wikipedia, of the 182 taxa of earthworms found in the United States and Canada, almost 33% are invasive species, being primarily from Europe and Asia. When they become too abundant, these non-native earthworms can lead to reductions in native plants species and some trees. This occurs when the worms move much of the decomposing organic nutrients from the soil surface down below the reach of the plants roots. By redistributing nutrients, mixing soil layers, and creating pores in the soil, they are also affecting the characteristics of the soil important to the rest of the ecosystem.