Life Cycle of Flies

The beginning of life is inextricably tied to the death and decay of another in the life of a fly. The family of flies is an extended one, over 250,000 species and sub-species are a part of the order of Diptera, two wing. In this genus, all insects have only one set of wings. This does not include many bugs whose names would lead you to believe they were a part of this category, such as butterflies, dragonflies and damselflies, these all have four wings, therefore are not true flies. Rather, this order includes mosquitoes, gnats and midges. The common housefly, musca domestica, is probably the most commonly known fly in this vast family.

The life of a fly begins when a female fly lays up to 500 eggs on her future children’s food source, organic material that is dead or decaying. At the moment of death, the scent of living tissue changes, this change is a signal to flies that a food supply for their young has just been created. Flies, heavy with eggs, seek out and find the scent of decay and can begin laying eggs within mere hours after death.

The eggs are white and minuscule, measuring 1.2 mm. Up to 500 eggs are laid in batches of 50 to 75 by the female. The day after being laid, the eggs hatch. Emerging from the white eggs are the larvae, maggots. The maggots live in and feed from the dead and decaying material they were laid on. With no legs, the maggots are bound to the site of their hatching, crawling only short distances. Growing rapidly and eating constantly, the larvae increase in size, up to 8 mm. Flies spend a week in the larvae stage, feeding and growing.

After one week, the maggot will crawl to a cool, dry place and transform into pupae. In the pupae phase, the fly is inactive and vulnerable. Only 8 mm long and a reddish brown color, the pupae is camouflaged while the final transformation of the fly takes place. Inside the hard shell, change is taking place rapidly, changing the legless maggot into the winged, legged adult fly.

The adult fly emerges from the pupae at their full growth, as any and all growth is done during the larval stage, while the fly was a maggot. A smaller fly is in essence an underfed maggot, and a large fly a well fed one. Size can be a determination of sex, however, the females being slightly larger than the males. An adult housefly is gray in color with black striping and a yellow colored underbelly. There are hair like spikes covering their entire bodies and they have two, large, red compound eyes, females eyes are spaced slightly farther apart than the males and a proboscis for feeding on a liquid diet as an adult. Food is liquefied through saliva and vomit. True to their order, they have one set of wings and small set of stabilizing protrusions called halterers, while flying these are moved rapidly to aid in steadier flying.

Living in adult form for up to a month, the female fly reaches maturity at 36 hours and is ready for mating. A female will only mate once in her life, but will store the sperm from that mating for laying several sets of eggs. The males are territorial and will mate with any female that comes into their range as well as will challenge other male flies that enter their territory.

While typically thought of as being caught inside a human dwelling, when outdoors a fly can travel several miles from their breeding place. Dependant on temperature, flies will move, breed and develop faster in warm weather and sunlight. Many flies remain in pupae stage over the winter, emerging in the spring.

The housefly, thought to have evolved 65 million years ago, has been around longer than man has had houses. With a fast life cycle and an abundance of food, humans will see the fly well into the future.