Common Housefly Life Cycle;

Each female fly can lay up to 500 eggs (in five batches of 100 eggs each). The eggs are white and are about 1.2 mm in length. Within a day, the larvae (maggots) hatch from the eggs; they live and feed in (usually dead and decaying) organic material, such as garbage or feces. They are pale whitish, 3-9 mm long, thinner at the mouth end, and have no legs. At the end of their third instar, the maggots crawl to a dry cool place and transform into pupae, colored reddish or brown and about 8 mm long. The adult flies then emerge from the pupae. (This whole cycle is known as complete metamorphosis.) The adults live from half a month to a month in the wild, or longer in benign laboratory conditions. After having emerged from the pupae, the flies cease to grow; small flies are not young flies but the result of insufficient food during the larval stage.
Some 36 hours after having emerged from the pupa, the female is receptive for mating. The male mounts her from behind to inject sperm. Normally the female mates only once, storing the sperm to use it repeatedly for several sets of eggs. Males are territorial: they will defend a certain territory against other males and will attempt to mount any females that enter that territory.


Housefly pupae killed by parasitic wasp larvae. Each pupa has one hole through which a single adult wasp emerged; feeding occurs during the wasp's larva stage.
The flies depend on warm temperatures; generally, the warmer the temperature the faster the flies will develop. In the winter, most of them survive in the larval or pupa stage in some protected warm location.
Some species of wasps can parasitize and kill the pupae.