Believe it or not, a great deal of the United States was earth-worm free prior to the arrival of Europeans. No native earthworms occured in the northern portion of the continental United States or anywhere in Canada except for a small section along the coast near the U.S. border. This absence of earthworms is believed to be due to Pleistocene glaciations -- probably the same force that limited the range of the American groundhog to the same eastern region earthworms were once limited to.
Approximately 70 species of native earthworms have been described from the eastern United States and another 28 species from the Pacific region. Another 45 imported species of earthworms are now commonly found in various parts of the U.S.-- mostly on the East Coast and in the Midwest and concentrated in areas with disturbed soils (i.e. regularly plowed fields).
Pictured is the native range of American earthworms.
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