In arctic Alaskan Toolik Lake, the predatory larval chironomid Procladius spp. (Diptera) feeds on a variety of benthic organisms including algae, other chironomids, and microcrustaceans. Laboratory experiments with two similar-sized chironomid prey, instar I Chironomus and instar II Paratanytarsus, showed that Procladius was a more effective predator on Chironomus. The two prey used different foraging behaviors; Chironomus grazed an area around its tube but Paratanytarsus remained inside its tube. In a field experiment, in which Procladius density was manipulated, a decrease in prey density occurred in the chironomid group Orthocladiinae, which could be attributed to Procladius predation. Gut analyses of Procladius showed that a higher proportion of Orthocladiinae was eaten than could be predicted from their abundance. Orthocladiinae, which typically graze around tubes, may have been more susceptible to Procladius because of behavioral characteristics.