Aquatic Insects of Michigan
by Ethan Bright, Museum of Zoology Insect Division and School of Natural Resources and Environment
Aquatic Isopoda (Sowbugs) of Michigan - Identification
Richard Snider (1991) published a review of the Isopoda of Michigan, and little work since then has been made to update this work. The great majority of the estimated 10,000 described species of isopods (sowbugs, pillbugs) are terrestrial or marine, but about 130 species of freshwater forms occur in North America north of Mexico. Williams (1972) provide a general survey of the freshwater fauna for North America, the majority of which in Eastern and Southeastern parts of the United States. Of the freshwater fauna, almost all of them are associated with some sort of lotic habitat, including springs, streams, and even subterranian habitats. Isopoda is quite depauperate in Michigan, with only 4 known freshwater species recorded from the state. The freshwater diversity of isopoda increases markedly in more eastern and southern states, particularly in regions of karst topography and Appalachian river systems.
Brown (1975) synonomyzed the species of Asellus with Caecidotea, although this may not be universally accepted.
The key below is modified from Williams (1972) and Pennak (1989).
Williams WD. 1972. Freshwater isopods (Asellidae) of North America. Water Pollution Control Research Series 180-50 ELDO/72, United States Environmental Protection Agency:1-45.