Doug,Great work on your prairie. Earthworm are getting a lot of attention in our area (Wisconsin). It turns out that nearly all of them are non-native. Apparently, with the exception of the Driftless region, there were no earthworms in the state due to the last glacial period. They are a concern in the northwoods as they quickly consume forest duff changing the plant and animal communities on the forest sueacar.Dfvid
Douglas Groothuis, Ph.D. 
Thank you for posting this.
Doug,Great work on your prairie. Earthworm are getting a lot of attention in our area (Wisconsin). It turns out that nearly all of them are non-native. Apparently, with the exception of the Driftless region, there were no earthworms in the state due to the last glacial period. They are a concern in the northwoods as they quickly consume forest duff changing the plant and animal communities on the forest sueacar.Dfvid