The bot fly larvae progress through three stages of development. Those three stages are known as instars. The time from egg laying to pupation is the total duration of the first two instars. During this time, the larvae migrate deeper into the tissue of the host. Incubation period within the host can take from 5 to 12 weeks. The third and final instar is known as the prepupal stage. During this final instar, the larva grows into a pupa.