Pests > House Fly
Common name: House Fly
Flies are among the fastest of all flying insects. The buzzing of a fly is the sound of its wings beating. A house fly's wings beat about 200 times a second, and some midges move their wings 1,000 times a second. House flies fly at an average speed of 4 and 1/2 miles (7.2 kilometers) per hour. They can fly even faster for short distances to escape their enemies, which include people and many birds.
There are about 100,000 kinds of flies. They make up an order (chief group) of insects. The scientific name of the order is Diptera, which comes from Greek words that mean two wings.
Distribution and Importance
The house fly is a well-known pest of both farm and home. This species is always found in association with humans or activities of humans. Not only are they a nuisance, but they also can transport disease-causing organisms. Excessive fly populations are obnoxious and a public health problem is possible.
More than 100 pathogens associated with the house fly may cause disease in humans and animals, including typhoid, cholera, bacillary dysentery, tuberculosis, anthrax ophthalmia and infantile diarrhea, as well as parasitic worms. Pathogenic organisms are picked up by flies from garbage, sewage and other sources of filth, and then transferred on their mouthparts and other body parts, through their vomitus, feces and contaminated external body parts to human and animal food.
Life Cycle and Description
The body of a fly
A fly's body has three main parts: (1) the head, (2) the thorax, and (3) the abdomen. The body wall consists of three layers and is covered with fine hair. Many kinds of flies have dull black, brown, gray, or yellowish bodies. A few kinds, including soldier flies and hover flies, may have bright orange, white, or yellow markings. Some kinds, such as bluebottle flies and greenbottle flies, are shiny blue or green. They seem to sparkle with brassy, coppery, or golden lights.
A fly has two large eyes that cover most of its head. The males of some species have eyes so large that they squeeze against each other. The eyes of most female flies are farther apart.
Like most other kinds of insects, a fly has compound eyes made up of thousands of six-sided lenses. A house fly has about 4,000 lenses in each eye. No two lenses point in exactly the same direction, and each lens works independently. Everything a fly sees seems to be broken up into small bits. The insect does not have sharp vision, but it can quickly see any movement.
A fly has two antennae that warn it of danger and help it find food. The antennae grow near the center of the head between the eyes. The size and shape of the antennae vary widely among different species of flies, and even between males and females of the same species. A house fly's antennae are short and thick; a female mosquito's are long and covered with soft hair; and a male mosquito's are long and feathery. The antennae can feel changes in the movement of the air, which may warn of an approaching enemy. Flies also smell with their antennae. The odor of the chemicals in rotting meat and garbage attracts house flies. The odors of certain chemicals bring vinegar flies to wine cellars.
The mouth of a fly looks somewhat like a funnel. The broadest part is nearest the head, and tubelike part called the proboscis extends downward. A fly uses its proboscis as a straw to sip liquids, its only food.
Flies do not bite or chew because they cannot open their jaws. Mosquitoes, sand flies, stable flies, and other kinds of "biting" flies have sharp mouthparts hidden in the proboscis. They stab these sharp points into a victim's skin and inject saliva to keep the blood from clotting. Then the flies sip the blood. Blow flies, fruit flies, and house flies do not have piercing mouthparts. Instead, they have two soft, oval-shaped parts called labella at the tip of the proboscis. The flies use these parts somewhat like sponges to lap up liquids, which they then suck into the proboscis. They sip liquids, or turn solid foods such as sugar or starch into liquids by dropping saliva on them.
A fly's muscles are attached to the inside wall of the thorax. These strong muscles move the insect's legs and wings. A fly has six legs. It uses all its legs when it walks, but often stands on only four legs. The legs of most kinds of flies end in claws which help them cling to such flat surfaces as walls or ceilings. House flies and certain other flies also have hairy pads called pulvilli on their feet. A sticky substance on the feet helps the insects walk on the smooth, slippery surfaces of windows and mirrors.
A fly's wings are so thin that the veins show through. The veins not only carry blood to the wings, but also help stiffen and support the wings. Instead of hind wings, a fly has a pair of thick, rodlike parts with knobs at the tips. These parts are known as halteres. The halteres give the fly its sense of balance. The halteres vibrate at the same rate as the wings beat when the insect is flying.
A fly is airborne as soon as it beats its wings. It does not have to run or jump to take off. In the air, the halteres keep the insect in balance and guide it so it can dart quickly and easily in any direction. A fly does not glide in the air or to a landing as do butterflies, moths, and most other flying insects. A fly beats its wings until its feet touch something to land on. If you pick up a fly, but leave the legs and wings free, the wings begin to beat immediately. Scientists sometimes do this with flies when studying wing movements.
A fly breathes through air holes called spiracles along the sides of its body. The abdomen has eight pairs of spiracles, and the thorax has two pairs. Air flows through the holes into tubes that carry it to all parts of the fly's body.
The life of a fly
A fly's life is divided into four stages: (1) egg, (2) larva, (3) pupa, and (4) adult. At each stage, the fly's appearance changes completely.
A female fly lays from 1 to about 250 eggs at a time, depending on the species. During her lifetime, one female may produce as many as a thousand eggs. The females of many species simply drop their eggs on water, on the ground, or on other animals. Some species stack the eggs in neat bundles.
At the tip of a female fly's abdomen is an organ called the ovipositor, through which the eggs are laid. The house fly usually places her ovipositor onto soft masses of decaying plant or animal material and lays her eggs there. One kind of mosquito arranges its eggs in groups that look somewhat like rafts. The eggs float on water until the larvae hatch.
The eggs of many kinds of flies are white or pale yellow, and look like grains of rice. A house fly's eggs hatch in 8 to 30 hours, but the time depends on the species of fly. Some kinds of mosquitoes lay their eggs during late autumn, but the eggs do not hatch until spring.
Larva of a fly is often called a maggot or a wriggler. The larvae of most kinds of flies look like worms or small caterpillars. They live in food, garbage, sewage, soil, water, and in living or dead plants and animals.
A fly larva spends all its time eating and growing. It molts (sheds its skin and grows a new one) several times as it grows. The larval stage lasts from a few days to two years, depending on the species. The larva then changes into a pupa.
Pupa is the stage of final growth before a fly becomes an adult. The pupae of mosquitoes and some other kinds of flies that develop in water are active swimmers. Most pupae that live on land remain quiet. The larvae of some flies build a strong oval-shaped case called a puparium around their bodies. Black fly larvae spin a cocoon for protection. Inside, the larva gradually loses its wormlike look and takes on the shape of the adult fly. Then the adult fly bursts one end of the pupal case or splits the pupal skin down the back and crawls out. The pupal stage of a house fly lasts from three to six days in hot weather, and longer in cool weather. The length of time varies among the different species.
When the adult emerges from the pupal case, its wings are still moist and soft. The air dries the wings quickly, and blood flows into the wing veins and stiffens them. The thin wing tissue hardens in a few hours or a few days, depending on the species, and the adult flies away to find a mate.
A fly has reached full size when it comes out of the pupal case. A small fly grows no larger as it gets older, even though its abdomen may swell with food or eggs.
Adult house flies live about 21 days in summer. They live longer in cool weather, but are less active. Most adult flies die when the weather gets cold, but some hibernate. Many larvae and pupae stay alive during the winter. They develop into adults in spring.
The housefly has a complete metamorphosis with distinct egg, larva or maggot, pupal and adult stages. The house fly overwinters in either the larval or pupal stage under manure piles or in other protected locations. Warm summer conditions are generally optimum for the development of the house fly, and it can complete its life cycle in as little as seven to ten days, and as many as 10 to 12 generations may occur in one summer.
Lifestyle and special aspects
The common house fly grows to approx. 6 – 9 mm in size; it smells excreted ferments with the feet and has a pronounced sense of smell. It also has so-called "adhesive pads" under the claws so that it can land upside down on the ceiling, for example. The common house fly lives on waste products, giving preference in particular to sugary products.
Egg: The white eggs, about 1.2 mm in length, are laid singly but pile up in small masses. Each female fly can lay up to 500 eggs in several batches of about 75 to 150 eggs, each over a three to four day period. The number of eggs produced is a function of female size, which is principally a result of larval nutrition.
Larva: The mature larva is 3 to 9 mm long, typical creamy whitish in color, cylindrical but tapering toward the head. The head contains one pair of dark hooks. The posterior spiracles are slightly raised and the spiracular openings are sinuous slits which are completely surrounded by an oval black border. The legless maggots emerge from the eggs in warm weather within eight to 20 hours, and they immediately feed on and develop in the material where the eggs were laid. The full-grown maggots have a greasy, cream-colored appearance and are 8 to 12 mm long. The larvae go through three instars. When the maggots are full-grown, they crawl up to 50 feet to a dried, cool place near breeding material and transform to the pupal stage. High manure moisture favors the survival of house fly larvae.
Pupa: The pupae are dark brown and 8 mm long. The pupal stage is passed in a pupal case formed from the last larval skin which varies in color from yellow, red, brown, to black as the pupa ages. The emerging fly escapes from the pupal case through the use of an alternately swelling and shrinking sac, called the ptilinum, on the front of its head which it uses like a pneumatic hammer.
Adult: The house fly is 6 to 7 mm long, with the female usually larger than the male. The eyes are reddish and the mouth parts are sponging. The thorax bears four narrow black stripes and there is a sharp upward bend in the fourth longitudinal wing vein. The abdomen is gray or yellowish with dark midline and irregular dark markings on the sides. The underside of the male is yellowish. The sexes can be readily separated by noting the space between the eyes, which in females is almost twice as broad as in males.
Adults suck liquids containing sweet or decaying substances. Larvae feed on moist food rich in organic matter. Although they are attracted to a variety of food material, house flies have mouth parts which allow them to ingest only liquid materials. Solid materials are liquified by means of regurgitated saliva.
The flies are inactive at night, with ceilings, beams and overhead wires within buildings, trees, and shrubs, various kinds of outdoor wires, and grasses reported as overnight resting sites. In poultry ranches, the outdoor aggregations of flies at night are found mainly in the branches, and shrubs, whereas almost all of the indoor populations generally aggregated in the ceiling area of poultry houses.
Flies commonly develop in large numbers in poultry manure under caged hens, and this is a serious problem requiring control. The control of Musca domestica is vital to human health and comfort in many areas of the world. The most important damage related with this insect is the annoyance and the indirect damage produced by the potential transmission of more than 100 pathogens associated with this fly.
Economic Injury Level
The threshold density for determining when to control flies depends on the area where the control measures will be taken. In general, at homes the threshold is very low and control actions are taken with few flies The complaint threshold density of the house fly at waste management sites may be 150 individuals per flypaper per 30 minutes.
House flies are monitored with baited traps, sticky ribbons, or spot cards on livestock facilities. Spot cards are 3-inch by 5-inch white index cards attached to fly resting surface. A minimum of five cards should be placed in each animal facility and left in place for seven days. A count of 100 or more fecal or vomit spots per card per week indicates a high level of fly activity and a need for control.
The more common control measures involved with the control of house flies are sanitation, use of traps, and insecticides, but in some instances integrated fly control has been implemented. The use of biological control in fly management is still at a relatively early stage.
Sanitation or Cultural Control: Good sanitation is the basic step in all fly management. Food and materials on which the flies can lay their eggs must be removed, destroyed as a breeding medium, or isolated from the egg-laying adult. Since the house fly can complete its life cycle in as little as seven days, removal of wet manure at least twice a week is necessary to break the breeding cycle. Wet straw should not be allowed to pile up in or near buildings. Since straw is one of the best fly breeding materials, it is not recommended as bedding. Spilled feed should not be allowed to accumulate but should be cleaned up two times a week. Ordinarily, fly control from 1 to 2 km around a municipality will prevent ingress of the house fly into a municipality.
Killing adult flies may reduce the infestation, but elimination of breeding areas is necessary for good management. Garbage cans and dumpsters should have tight-fitting lids and be cleaned regularly. Dry garbage and trash should be placed in plastic garbage bags and sealed up. All garbage receptacles should be located as far from building entrances as possible.
Traps: Fly traps may be useful in some fly control programs if enough traps are used, if they are placed correctly, and if they are used both indoors and outdoors. House flies are attracted to white surfaces and to baits that give off odors. Indoors, ultraviolet light traps collect the flies inside an inverted cone or kill them with an electrocuting grid. One trap should be placed for every 30 feet of wall inside buildings, but not placed over or within five feet of food preparation areas. Recommended placement areas outdoors include near building entrances, in alleyways, beneath trees, and around animal sleeping areas and manure piles. Openings to buildings should be tightly screened with standard window screen, thereby denying entrance to flies.