mosquito hawk

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. See nighthawk.
2. n. Lower Southern U.S. See dragonfly. See Regional Note at dragonfly.

Century Dictionary and Cyclopedia

1. n. A dragon-fly. The name applies to any of these insects in the United States, from their preying upon mosquitos and other gnats. This habit is so well marked that propositions have been made for the artificial propagation and protection of dragon-flies as a means of relief from mosquitos in places where the latter are exceptionally numerous.
2. n. The night-hawk, a caprimulgine bird, Chordeiles popetue, or some other species of the same genus.

Wiktionary

1. n. US, regional A dragonfly.

GNU Webster's 1913

1. n. (Zoöl.) a dragon fly; -- so called because it captures and feeds upon mosquitoes.

WordNet 3.0

1. n. mainly nocturnal North American goatsucker
2. n. slender-bodied non-stinging insect having iridescent wings that are outspread at rest; adults and nymphs feed on mosquitoes etc.