Found worldwide. There are over 5150 species, and 282 British species. Most feed on liquids by lapping them up with their spongy mouthparts (see right), but there are a few blood-suckers and predators in the family. The larvae feed mainly on dung and decaying matter. Many are pests of livestock and vectors of disease. Most British adults are grey or black.
Although it is true that if all humans disappeared tomorrow most insects would survive, the Common house fly would not be one of the survivors. Without us and our domesticated animals it would soon die out.
Above are the lapping mouthparts of a house fly.
Female house flies usually mate just once, whilst males mate as often as they can and are pretty indiscriminate in their choice of partner. They will attempt to mate with anything that resembles a female house fly, and that includes male house flies and other similar looking species.. The male grabs hold of any prospective mate and tastes them to see if they'll do. He tastes with his feet. Courtship is brief, and mating usually takes place at rest, although, if they are disturbed the female can fly off for a short distance with the male clinging on to her back.
The female deposits her white, cigar-shaped eggs in manure or rotting refuse. The cigar-shaped egg is around 1 mm long and glistening white. They are laid in batches of 12 - 150, and a female can lay up to 900 eggs in her lifetime. She will lay every 10 days or so. In theory one pair of adults could give rise to 190 million billion flies in 3 - 4 months!
Within 24 hours the white legless larva or maggot (see above) hatches and starts to eat its surroundings. Before another 24 hours have passed it has grown so much in size that it must moult its skin. Under normal circumstances it eats so much and so quickly that it moults 3 times in 3 days. A fully grown larva is 10 - 12 mm long. The head end is small and pointed. Then on the fourth day it crawls away and burrows underground where it pupates for about 3 days. It can burrow up up to 30 cm deep to pupate. In the drawing on the left it is the pointed end that is the head. It can withdraw its head into its body for protection.
The pupa is barrel-shaped, pale yellow at first, but darkens to brown/black. So from egg to adult takes around a week to 10 days. The adult fly emerges from the more pointed end of the pupal case.
The adult fly (see above) emerges, tunnels upwards to the surface to begin its adult life which lasts around 2 months. The body length is from 3 - 12 mm. It has a grey body with 4 black lines down its thorax. Within a week of hatching into an adult the female, once mated, is ready to lay her first batch of around 100 eggs. The adult feeds off rotting garbage as well as fresh food, and because of its pads of sticky hairs on its feet (see the drawing on the right) it picks up and spreads germs. It is a carrier of typhoid, dysentery, diarrhoea, and in warmer regions cholera, yaws and opthalmia.
Foot. The leg ends in 2 claws (see above), each with a hair-covered pad underneath. When the pad is pressed the hairs exude a sticky fluid, so enabling the fly to walk on most surfaces.
The biggest predators of house flies, apart from man, are spiders, toads, lizards and birds. Flight speed has been recorded as 2.0 metres per second with a wing beat of 190 per second. Compare this with other insects.
Its mouthparts are soft and end in spongy pads, see above, and it feeds only on liquids. So how does it feed off a sugar lump or other solids? Well it regurgitates part of its last meal on to its next meal. This liquid and the enzymes in it soften and liquefy part of the solid which the fly then mops up. Part of its last meal may have been faeces, carrion or other rotting organic matter. This it vomits up with some of its gut bacteria. This is another way of spreading germs. Also it frequently defecates while feeding.
It has been found that 5 million bacteria can be found on the body surface of a single adult! It has also been found that an individual will fly as far as 20 miles to reach a good source of food. So the fly that landed briefly on your sugar bowl or, even worse, on the rim of your glass, can easily have flown from any source of sewage or manure within a 20 mile radius.
Like most adult insects it has 2 compound and 3 simple (ocelli) eyes.
Overwintering. Most adult houseflies will die with the onset of cold weather, however some can survive the winter, and some will overwinter as pupa.
Deception. On an island off the Sardinian coast the dead horse plant, an arum lily, Helicodiceros sp. gives off a perfume of rotting meat. This attracts blow flies who normally lay their eggs on rotting meat on which the larvae need to feed when they hatch. The flies land on the plant and make their way to the source of the smell inside the flower. The structure inside is very elaborate, and on the way down there are guard hairs prohibiting escape. The flies are trapped inside the flower. The flies can feed on nectar and lay their eggs, however the larvae will die as there is nothing for them to feed on when they hatch. On the second day the stamens shower the captive blow flies with sticky pollen. And on the third day the guard hairs wither and the flies can escape to pollinate other Helicodiceros as the pollen rubs off their bodies as they make their way down inside another flower.
Above and below is Mesembrina meridiana one of the largest British Muscids. The adult reaches 10 - 12 mm long. It is often found sunbathing on walls and flowers from early spring until late autumn. It is especially fond of umbelliferous flowers where it drinks nectar.
The female lays her eggs singly in horse or cow dung. The egg is 4.5 mm long, and hatches almost immediately.
Above is a close up of the yellow patches on the face, and below the claws and pads of the foot.