Generalized life cycle of flies causing myiasis in humans based on Human Bot Fly (click on image for description of variations)
Adults of the Human Bot Fly Dermatobia hominis are free-living flies (1). Adults capture blood-sucking arthropods (such as mosquitoes) and lay eggs on their bodies, using a glue-like substance for adherence (2). Bot fly larvae develop within the eggs, but remain on the vector until it takes a blood meal from a mammalian or avian host. Newly-emerged bot fly larvae then penetrate the host's tissue (3). The larvae feed in a subdermal cavity (4) for 5-10 weeks, breathing through a hole in the host's skin. Mature larvae drop to the ground (5) and pupate in the environment. Larvae tend to leave their host during the night and early morning, probably to avoid desiccation. After approximately one month, the adults emerge (6) to mate and repeat the cycle. Other genera of myiasis-causing flies (including Cochliomyia, Cuterebra, and Wohlfahrtia) have a more direct life cycle, where the adult flies lay their eggs directly in, or in the vicinity of, wounds on the host (7). In Cochliomyia and Wohlfahrtia infestations, larvae feed in the host for about a week, and may migrate from the subdermis to other tissues in the body, often causing extreme damage in the process.
From Centers for Disease Control Parasites and Health website