Rodent Bot Fly

Cuterebra fontinella (family Oestridae) is a large, robust, bee-like fly 15-25 mm long, with a densely hairy dark body, small head, and vestigial mouthparts. Adults do not feed and live only 1-2 weeks, relying entirely on fat reserves accumulated as larvae. Females deposit sticky eggs near rodent burrow entrances, runways, and nest openings rather than on the host. Body heat from a passing host triggers hatching within seconds; the first-instar larva enters through the nose, mouth, eyes, or a wound, then migrates to a subdermal site where it forms a breathing warble. Larvae feed for 19-38 days, exit to pupate in soil, and overwinter as pupae.

Adults are non-biting, harmless, and rarely seen; males hilltop and defend sunlit perches while waiting for females. The pest significance lies with the larvae, which cause obligate subcutaneous myiasis (warbles) in mice, rats, chipmunks, squirrels, and rabbits. Domestic cats and dogs that hunt rodents can be accidental hosts, most often developing a swelling with a visible breathing pore on the neck or head; aberrant migration can rarely reach the eye or central nervous system. Human cases are very rare and typically follow contact with infested rodent habitat.