Just because we have native earthworms, though, doesn't mean that the invasives aren't a problem.  We've introduced species from elsewhere for bait, vermicomposting (gulp!), and accidentally in plant roots.

The biggest problems from these invasive earthworms is occurring in previously glaciated areas where native earthworms don't occur.  There, invasive earthworms are totally changing soil dynamics by eating up the duff (leaf litter) on the forest floor, which in turn affects the trees and wildflowers which grow there.

Even down here in the South, we have invasive earthworms.  When competing with native earthworms, invasives tend to gain a foothold in disturbed and fragmented forests.  Scientists are beginning to realize that invasive earthworms down here may be linked to the spread of invasive plants like the extremely troublesome Japanese Stiltgrass and might also compete with our forest salamanders.