Flies can be found almost anywhere you look.
"Fly" is the common name for all insects in the order diptera. This basically includes all insects with two wings. You are probably familiar with mosquitoes, black flies, midges, fruit flies and blowflies--all members of the diptera order. Though the cycle is the same, development times vary between species and change with temperature. They live everywhere in the world except Antarctica.
Eggs
Flies begin as an egg before hatching into larvae and pupating into adults. Flies lay eggs all over the place, usually in clumps of about 300, but most commonly in dead and decaying remains. Flies remain in the egg for one day before hatching.
Larvae
Larvae move through three instars (life stages) before pupating. During the first instar, the larva feeds on fluid excreted from the organic remains. The time from hatching to first molt is one day. In the second, the larvae move around in a maggot mass for one day before the second molt. In the final instar, the larva gets much larger, but still moves around in the maggot mass. The fly takes two days to move from the second molt to the pre-pupa stage.
Pre-Pupa
During the pre-pupa stage, flies do not feed. The fly focuses on moving from the corpse into the soil and finding a pupation site. Once it finds a site, the fly takes four days to transform from pre-pupa into pupa while it creates its puparium, a skin similar to when a caterpillar is spinning its chrysalis.
Pupa
Pupas live in the puparium, which hardens into a larval skin or case. The pupa does not feed, but instead puts all its energy into transforming from the larval body to the adult fly. The pupa hides inside the hardened skin of the last larval stage and does not emerge as an adult fly for 14 days.
Adult
The adult fly emerges from the pupa and immediately mates. It feeds on protein from body fluids during its two-day life. At the end of 48 hours, the fly lays its eggs on a corpse and then dies. Adult flies have reduced hind wings that act as balancing agents during flight. The mouthparts have large fleshy pads with drainage canals for liquids. Some flies have mouthparts designed for stabbing other insects, and the mosquito mouth can pierce vertebrate skin to remove blood and additional fluids.
Forensics
The fly life cycle is very useful to scientists when determine the age of a corpse, specifically in forensic science. Since the fly life cycle is predictable, and they find bodies very quickly, their behavior allows scientists to accurately determine the time of death. After taking into account the environmental conditions, all they need to do is count back the days required for the development of flies living on the corpse.
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