This is a most interesting question. Yes, there are species of invasive earthworms here in the U. S., mostly from Europe and Asia. Back in 2007, Ira Flatow of NPR's Science Friday had an interview with Peter Groffman, senior scientist at the Institute of Ecosystem Studies in Millbrook, New York, about invasive earthworms. They are responsible for negative changes in local ecosystems.
I think you'll find it most interesting. Are any of your neighbors noticing changes? I would check with the Chester County Agricultural Extension Service to see whether this is a problem in your area which has been reported or documented. Here is how to reach that office:
601 Westtown Road, Suite 370
Government Services Center
West Chester, PA 19380-0990