Eastern chipmunks (Tamias striatus L.) were placed in Plexiglas cages with 0, 2, 5, 10, or 20 female Aedes triseriatus Say mosquitoes for 2 h. Previously published studies demonstrated little effective mosquito defensive behavior because of pause behavior by the chipmunks. By recording chipmunk behavior on videotape, pause behavior was reduced, and the chipmunks exhibited effective mosquito defense. The chipmunks defended themselves actively by attacking mosquitoes in flight, biting, head shaking, body turning, face grooming, hindfoot scratching, and flicking the tail. These defensive behaviors were correlated positively with the number of mosquitoes exposed to the chipmunks and with the number of mosquitoes killed.