True Flies are found everywhere, and include delicate craneflies, mosquitoes, and midges, as well as robust horseflies, house flies and blowflies.
Many sorts of insects are described as flies but "true flies" are a distinct group of insects which have only one pair of wings, unlike the caddisflies, scorpion flies, mayflies and butterflies that have two pairs of wings.
There are many species of true fly with medical, veterinary, and agricultural importance. Biting, blood-feeding flies such as mosquitoes, midges, horseflies and blowflies are able to transmit diseases to humans and domestic animals. Fruit flies and leaf mining flies damage fruit and crops. But most flies are not pests, most are important decomposers of plant and animal matter. Many flies are predators and parasites of other insects, and some are used in the biocontrol of insect pests and weeds.
Flies come in many shapes and sizes. Some are difficult to recognise as flies as they mimic other invertebrates such as wasps, beetles and spiders.
Flies belong to the Order Diptera. In Australia there are almost 7500 described species in 100 families. However, some suggest that only 25% of Australia's fly species are described and have proper scientific names.
The large crane fly Nephrotoma australasiae is not a mosquito. There are more craneflies (over 700 species) in the family Tipulidae than in any other group of flies in Australia.
Mosquitoes like Aedes vigilax (Family Culicidae) are true flies as they have one pair of wings.
A predacious mosquito wriggler, Toxorynchites speciosus.
The wasp mimicking Adapsilia illingworthana (Family Pyrgotidae).
The Green Signal Fly, Lamprogaster imperialis (Family Platystomatidae), has a bright metallic green thorax and abdomen and wings patterned with dark spots and streaks.
American Soldier Flies, Hermetia illucens (Family Stratiomyidae), look and even behave like wasps.
The bush fly, Musca vetustissima (Family Muscidae), has short, three-segmented antennae.
Flies have only one pair of wings, the forewings. Unlike all other insects, their hindwings are reduced to tiny dumbbell-shaped knobs called halteres, which are used for balance during flight.
The antennae are long and often threadlike in more primitive flies and very short with only three segments in houseflies and blowflies.
Fly larvae have no legs, and are often referred to as maggots.
The white dumbbell-shaped left haltere, all that remains of the hindwing, can be seen above the midleg on this fly from the Family Heleomyzidae.
Some fly larvae are maggots, including those of fruit flies (Family Tephritidae).
Many fly larvae do not look like maggots, including this mosquito wriggler (Ochlerotatus notoscriptus).
Adult flies usually feed on fluids or solids that they liquefy with saliva and then suck up using a spongy proboscis. Females of some flies, such as mosquitoes, biting midges, bird flies and horseflies, feed on blood. They need a meal of blood to mature their eggs. Some adult flies are voracious predators feeding on insects and other invertebrates.
Flies undergo abrupt metamorphosis. Most flies have several larval instars and a pupal stage before emerging as winged adults. Most fly larvae are decomposers, feeding on decaying plant or animal matter. Some feed on living plants such as fruit flies. Some larvae are predators such as those of robber flies and hover flies. Others, such as beeflies and bristle flies, are internal parasites of the larvae other insects. A few are parasites of vertebrates, living in open wounds or pockets beneath the skin or internally in nasal cavities and the intestinal tract. Several of these species, for example blowflies, are medically important parasites of humans or domestic stock.
The spongy proboscis of a Green Signal Fly, Lamprogaster imperialis.
A bird fly, Ornithomyia fuscipennis (Family Hippoboscidae). These spider-like flies are external parasites that suck the blood of large birds such as owls, frogmouths, birds of prey and kookaburras.
Predatory Giant Robber Flies, Blepharotes spp. (Family Asilidae) are strong flyers, catching insects on the wing.
The dance fly Austrosciapus connexus (Family Dolichopodidae) often lands on leaves in gardens where it preys on small, soft-bodied insects.
The flattened, leathery larvae of the American Soldier Fly, Hermetia illucens (Family Stratiomyidae), are often found in compost heaps.
Passeromyia indecora (Family Muscidae) maggots are parasitic upon nestling birds.
Bristle flies of the genus Rutilia (Family Tachinidae) have parasitic larvae that develop within the grubs of scarab beetles.
The spiky, brown larvae of this beefly, Thraxan sp. (Family Bombyliidae), are parasites within the nests of mud dauber and potter wasps.