Flies and Gnats

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Everyone is familiar with house flies (order Diptera). They aren't the cleanest of insects--they visit dumps, sewers, and garbage heaps. They feed on fecal matter, discharges from wounds and sores, sputum, and all sorts of moist, decaying matter like spoiled fish, eggs, and meat.

Flies regurgitate and excrete wherever they come to rest and thereby are ideally suited to mechanically transmit disease organisms. House flies are suspected of transmitting at least 65 diseases to humans, including typhoid fever, dysentery, cholera, poliomyelitis, yaws, anthrax, tularemia, leprosy, and tuberculosis.

Biology

People often confuse house flies with a lot of closely related flies. House flies are easy to identify. They have four dark longitudinal stripes on top of the thorax, or middle body region. They vary in length from 1/8 to 1/4 of an inch.

The mouth parts of the house fly are adapted for sponging up liquids. They cannot bite, but a similar-appearing stable fly can bite. Flies ingest only liquid food. They feed on solid food by regurgitating saliva onto it. The saliva liquefies the solid material, which is then sponged up with the proboscis. They require water since they continually salivate and void liquids. Fly specks seen on surfaces visited by house flies are the excreted wastes. hyg-30-a.gif - 6.2 K

Female house flies deposit their eggs in decaying matter such as grass clippings, garbage, and human and animal excrement. Horse manure is the preferred breeding medium. Each female deposits about 100-150 eggs on appropriate food. Eggs can hatch in 7 1/2 hours when temperatures are high (about 99 degrees F), or it can take up to 2 days in lower temperature.

Eggs hatch into worm-like creatures called maggots. Maggots lack definite heads, eyes, antennae, and legs. Their bodies are pointed at the front end and gradually widen at the rear. Fly maggots feed on the material in which they find themselves.

Following three larval molts, mature larvae stop feeding and burrow into drier surrounding areas, where they pupate. The pupa is a chestnut brown, oval object within which the larva changes into an adult house fly. Adults mate within one to two days after emerging from their pupal cases. The life cycle from egg to adult can happen in as little as one week, but typically it takes three weeks.
House flies normally live about 2 1/2 weeks during the summer, but they can, at lower temperatures, survive up to 3 months. Some overwinter outdoors in protected locations, or in crevices in buildings. Flies normally stay within 1/2 mile to 2 miles from their point of origin, but some have been known to travel as far as 20 miles to find food and a place to lay eggs.

Control

The four basic principles of house fly control in order of lasting effectiveness are sanitation, exclusion, non-chemical measures, and chemical methods.

Sanitation

Flies can't breed in large numbers if food sources are limited. Don't allow materials such as manure, garbage, weed piles, grass clippings, or other decaying organic matter to accumulate. Keep trash cans clean and tightly covered. Be careful not to wash garbage cans where the rinse water might drain into the soil; flies can breed in soil full of organic matter. Dry out maggoty garbage or dispose of it in fly-proof containers or landfills.

Exclusion

Flies can be kept outside of homes by the use of window and door screens. Make sure screens are tight fitting and without holes. Keep doors closed, making certain there are no openings at the top or bottom. And check for openings around water or gas pipes or electrical conduits that feed into the building. Caulk or plug any openings. Ventilation holes can also serve as a route for flies to enter a building. Ventilation is necessary to keep adequate air circulation in a building, but use screening to exclude flies.

Non-chemical Measures

The use of devices like ultraviolet-light traps, sticky fly traps, fly swatters, and baited fly traps can eliminate many flies inside a home, but the fly swatter is an economical control method for the occasional fly.

Chemical Control

If you have lots of flies inside your home, use a space spray (aerosol) labeled for flying insects. Most space sprays contain pyrethrins for quick knockdown, but aerosols give only temporary relief. Find out why flies are there. Then take steps to get rid of them through sanitation and exclusion methods.

Midges and gnats

are common names for a large number of small, non-biting flies. Many species look like mosquitoes and may form annoying swarms or clouds in the air but they do not bite. The immature stages develop in water in pools, containers, ponds, clogged rain gutters, or in some cases, wet soil or seepage areas. Most feed on living or decaying plant matter and are an important part of aquatic food chains. Many species can survive in very stagnant or polluted water.

midge swarm
Large mating swarms of adults often appear about dusk and may occur for several days, especially after a prolonged wet period. Many gnats are attracted to light and may be a nuisance, landing on people or entering homes or businesses. These tiny flies do not feed. They only live long enough to mate, lay eggs, and die. Eggs are laid in masses in the water or on aquatic vegetation. The life cycle usually takes about 4 to 5 weeks. There may be several generations during the summer but these insects usually disappear with the onset of dry weather. Fortunately, problems are usually temporary and intermittent.

There are no good alternatives for control of the adults, other than some pressurized aerosol sprays containing pyrethrins. These are impractical for treating anything other than small areas. These products only kill insects that are directly hit by spray particles; there is no lasting or residual effect. More gnats will quickly enter the area after the spray has settled. The gnats rest on vegetation and in the grass during the day, so an application of a Cythion (malathion) or Sevin (carbaryl) spray may reduce numbers somewhat.

Long term control requires trying to eliminate breeding sites, wet areas or standing water. Often, however, this is not practical. Water should not be treated with any insecticide in an attempt to control gnats. The potential harm to the environment and wildlife is too great to justify an application for a temporary nuisance.