Flies belong to the fourth largest animal order, Diptera, which comprises 95,000 species of two-winged insects. The Diptera evolved from four-winged insects, and their vestigial rear wings are stalks that act as gyroscope balance organs, enabling the forewings to move the fly forward without causing nose dives, and keeps it on a steady course. Dipterans occur worldwide, including Antarctica, but are most plentiful in moist,warmclimates. The main dipteran suborders are Nematocera, Brachycera, and Cyclorrapha. Nematocera are mosquitoes, slender, with long antennae. The other orders have stout bodies and short antennae; among them are houseflies and tsetse flies.
Physical Characteristics of Flies
Afly body has three parts: a head, thorax or middle part that holds six legs, and an abdomen or rear end. Two compound eyes containing up to four thousand facets cover most of the head. The eyes see light changes and sudden movement from many different directions at once. This is why flies are hard to catch Atop a fly's head, paired antennae provide the senses of touch and smell. Dipterans have a mouth part called a proboscis. It is funnel-shaped, with its wide part at the bottom. The proboscis is like a straw, sucking up fluid via a pump in the head. The proboscis of a housefly is soft, so it cannot bite. Bee flies have a long proboscis that enters flowers for nectar. Biting flies, such as horseflies, have hard, sharp proboscises that pierce the skin of their victim. Each foot on a fly is tipped by claws that grip rough surfaces. Under the claws are pads called pulvilli. On smooth surfaces, they flatten and grip tightly, allowing a fly to walk upsidedownon ceilings without falling. Flies breathe through openings called spiracles, located on each side of thorax and abdomen.
The life of a fly begins when a female lays hundreds to thousands of eggs in manure, garbage, vegetable waste, fruit, plant stems, or stagnant water. Houseflies have telescoping ovipositors that place eggs in soft matter. Other species have stiff ovipositors that penetrate plant stems or fruit. Flies, like mosquitoes, also lay eggs on water. The heat given off in these environments incubates the eggs. In one or two days they hatch as white, legless larvae (maggots), which eat the material surrounding them. Maggots rapidly grow too large for their skins, which split and allow molting. After molting twice, the larvae find sheltered places to form pupariums, where they molt a final time and become pupae, and then become winged flies. The process usually takes four to ten days. Adult flies emerge from the pupae fullsized. Most live for thirty days. In winter most die, but larvae and pupae live to become adults in the spring. The development of a fly from egg, to larva, to pupa, to adult is called metamorphosis.
Tsetse Flies, Horseflies, and Blowflies
Tsetse flies are twenty species of genus Glossina. Five of these species carry sleeping sickness. They live in grasslands, forests, and river and lake shores in Africa, between the Sahara and Kalahari deserts. Tsetse flies suck blood with their sharp proboscises; the blood is digested with the assistance of a membrane that is secreted around the blood meal in the foregut. Tsetse flies mate year round. Females have one offspring per mating. After fertilization, an egg hatches in the mother and is later born as a full-sized maggot, which burrows into the soil, pupates, and becomes adult in a month. The flies carry trypanosomes that can infect people with sleeping sickness. When the tsetse fly bites a victim, the trypanosomes enter, multiply, make them very tired, and quickly kill them. The 3,500 Brachycera species of horseflies occur worldwide, most in tropical and temperate fields and forest areas near water. They have inchlong, stout bodies, large heads, short antennae, and iridescent compound eyes. Their mouths pierce the surfaces of plants and animals to suck fluids. Males eat nectar and plant juices, while females suck blood. The time of mating varies according to species and climate. Females must eat blood before laying eggs or the eggs do not develop. A female lays one thousand eggs in damp sites such as rotten wood. Larvae hatch in two to three weeks, although some hibernate all winter. Before becoming adults, larvae pupate for about three weeks. Adults live for six weeks before mating and dying. Horsefly bites are painful and may cause anthrax or tularemia.Blowflies are metallic blue-green and are larger than houseflies. Females lay eggs on meat or in the open wounds of animals. Eggs or larvae that are in food swallowed by animals and humans cause pain and sickness when the maggots eat into the wound or tissue where they were laid. When the larvae enter an animal's skin, puss-filled sores form. The screwworm, a blowfly larva, harms livestock. If screwworms are not controlled, animals die.
Flies and Disease
A housefly can carry pathogenic bacteria disease because it lives in manure and garbage. Thousands of related species transmit germs to whatever surface they land on, spreading disease. Often it is best to kill flies and stop their reproduction. Flies destroy crops; parasitize animals; and carry typhoid and cholera. However, flies are also useful. Some flies, such as hoverflies, pollinate plants. Larvae also eat aphids, which kill crops. Flies speed the decomposition of animal carcasses and manure. In addition, flies consume other harmful insects, controlling their numbers. Finally, flies are the food source for numerous insectivores higher up the food chain.
Suborder: Brachycera, thirty-five families
Geographical location: Every continent
Habitat: Grasslands, forests, near rivers and lakes
Gestational period: Eggs hatch in two to seven days; adulthood occurs in one to six weeks
Life span: One to six months
Special anatomy: Six legs; compound eyes; one pair of wings, antennae, proboscises; pulvilli
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