Lifecycle of a blow fly
Blow fly maggot
Blow fly puparium
Blow fly (Phaenicia sericata)
Adult Black Blow Fly and Puparia (Phormia regina)
Photomicrograph of mandibular sclerite of maggot, 1935
Photomicrograph of left posterior stigma of maggot, 1935
Blow fly puparium
Blow fly puparium
Larvae of different species move different distances from the body prior to pupariation, some as much as 8 meters. The larvae becomes shorter and stouter and the outer cuticle (skin layer) of the larvae hardens into the puparium and slowly darkens over a period of about 10 hours. Adults will emerge between 77 and 134 hours after pupariation depending on the temperature.
Cleveland Museum of Natural History
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Life cycle of the black blow fly

Adult female blow flies arrive within minutes to lay eggs on a cadaver. Each deposits about 250 eggs in the natural openings of the body and open wounds. The eggs hatch into first-stage maggots within 24 hours. These feed and then molt into second-stage maggots, which feed for several hours, and then molt into third-stage maggots. Masses of third-stage maggots may produce heat, which can raise the temperature around them more than 10° C. After more feeding, the third-stage maggots move away from the body and metamorphize into adult flies.