These photos supplement pages 77-86 of the Guide to Aquatic Invertebrates of the Upper Midwest. Information on the biology of Perlodidae can be found on page 85. Perlodidae have beautiful patterns like Perlidae, however they lack branched gills on their thoracic segments. Click to compare with Perlidae. The most distinctive character for Perlodidae is the fact that hind wing pads diverge from the body axis as seen below.