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Hydrophilidae is the second most diverse family of aquatic beetles in Alberta, exceeded only by Dytiscidae. Adults are separated from adults of other aquatic beetles by a combination of features. Unlike dytiscid adults, hydrophilid adults (and adults of the other Alberta families except Dytiscidae, Amphizoidae, Gyrinidae and Haliplidae) do not have the hind coxae (the basal part of the leg connecting the leg to the body) extending posteriorly to divide the first abdominal sternite (the ventral part of the first abdominal segment). This is easy for me to say, but it takes practice and comparisons of adults of different families to distinguish this feature. Once determined that the first abdominal segment is not divided by the hind coxae, it is simply a matter of determining that the antenna is clubbed. If so, and the specimen is over about 3 mm in length, it probably is a hydrophilid. Hydraenidae adults have these features of hydrophilids, but they are rarely over 2 mm in length. We have at least 15 genera of aquatic Hydrophilidae in Alberta. Adults and larvae never seem to occur in large numbers. Life cycle features apparently have not been studied in Alberta. The family is called water scavenger beetles, but larvae are mainly predacious, and adults of many species are herbivorous. Several criteria are usually needed to separate hydrophilid adults even to the genus level. The purpose here is simply to emphasize their diversity. The photo specimen is Ametor scabrosus, about 7 mm in length. Photograph: From page 385 of Clifford, Hugh F. 1991. Aquatic invertebrates of Alberta. University of Alberta Press, Edmonton, Alberta, 538 pages. (Source: University of Alberta BioDiTRL online database, accessed Dec. 7, 2015. Copyright restrictions apply.)