Larvae of Cucujus clavipes (Fabricius) and Dendroides canadensis (Latreille) are frequently found under bark of decaying hardwood logs and those of Pytho depressus (Linnaeus) under that of dead conifers, especially pine (Pinus spp.) (Anderson and Nilssen 1978). Larvae of all three species have a dorsoventrally depressed, orthosomatic body and are well adapted for activity in the cambial layer. In dead trees, this area contains partially decomposed wood and bark resulting from the activity of phytophagous insects and other small invertebrates. According to textbooks of general entomology and other entomological literature, species within the genera Cucujus, Dendroides, and Pytho are predacious on other insects found in the cambial layer (Arnett 1968; Borrer et al. 1976; Borror and White 1970; Essig 1926; Peterson 1951; Swan and Papp 1972). However, no specific references to original studies demonstrating this type of feeding behaviour could be found. The purpose of this study was to determine the type of food consumed by larvae of these species and to determine if the structure of their mandibles and other mouthparts were indicative of such food consumption.