PREDACEOUS DIVING BEETLES IN MAINE: FAUNAL LIST AND KEYS TO SUBFAMILIES

In 1935 in Tremont, Maine, a man reported that his trout were being eaten by lizards (Procter 1946). The piscivorous culprit was identified, not as a lizard, but as a larval predaceous diving beetle, which resembled an alien space monster in a Calvin and Hobbs cartoon. The heads of these larvae are flat, armed with long, sickle-shaped mandibles (Plate I), and the mandibles are deeply grooved or often hollow (Plate II-b), which allows the larvae to inject digestive juices into prey and then suck predigested body tissue from the prey for nourishment. Larvae of predaceous diving beetles will attack and feed on any animal they encounter. Drummond and Wolfe (1981) witnessed the successful attack by a Dytiscus larva (length 50 mm) on a garter snake, Thamnophis elegans (length 192 mm; weight 2.8 g). The snake writhed convulsively for 7 minutes before dying. This tenacity of the larvae of this family has earned them the appropriate title of "water tigers." Although beetles are primarily terrestrial (350,000 species world wide), 5,000 species are aquatic and 60 percent of these are predaceous diving beetles. Of the 25,000 species of beetles living north of Mexico, approximately 900 are aquatic and of these, 446 species are in the family Dytiscidae (Lawrence 1991). The largest study providing information on predaceous diving beetles in Maine is by Procter (1946). This survey, which encompassed Acadia National Park, documented 33 species of diving beetles. A more comprehensive survey of the entire state completed by Malcolm (1971) added another 14 species to the faunal list and documented 43 species that he expected to be in Maine, but had not yet been collected . The number of species reported from Maine (i.e., 67) is probably fewer than exists in