Filth-Breeding Flies

P. G. Koehler and F. M. Oi

Several kinds of non-biting flies can be found in and around farms, residences, and food-handling establishments. These flies can be harmful to health, causing annoyance and discomfort. All filth flies have an egg, larva (maggot), pupa, and adult stage in their life cycle. The adult fly has 2 wings (the hind pair is reduced to a knobbed balancing organ).

Filth flies are usually scavengers in nature and many are capable of transmitting diseases to man. Filth flies can usually be grouped according to their habits and appearance as: houseflies and their relatives; flesh flies, blow flies and bottle flies, filter flies, soldier flies, and vinegar (fruit) flies.

House Fly

The house fly, Musca domestica  is one of the most common of all insects. It is worldwide in distribution and is a pest in homes, barns, poultry houses, food processing plants, dairies, and recreation areas. It has a tremendous breeding potential and during the warmer months can produce a generation in less than two weeks. In many areas of Florida the house fly breeds continually throughout the year.

House fly eggs are laid in almost any type of warm organic material. Animal or poultry manure is an excellent breeding medium. Fermenting vegetation such as grass clippings and garbage can also provide a medium for fly breeding. The whitish eggs, which are laid in clusters of 75-100, hatch within 24 hours into tiny larvae or maggots. In 4 to 6 days the larvae migrate to drier portions of the breeding medium and pupate. The pupa stage may vary in length considerably, but in warm weather can be about three days. When the adult emerges from the puparium, the wings are folded in tight pads.

The house fly crawls about rapidly while the wings unfold and the body dries and hardens. Under normal conditions this may take as little as an hour. Mating occurs immediately. A house fly may go through an entire life cycle; egg, larva, pupa to winged adult in 6 to 10 days under Florida conditions. An adult house fly may live an average of 30 days. During warm weather 2 or more generations may be produced per month. Because of this rapid rate of development and the large numbers of eggs produced by the female, large populations build up.

House flies are strong fliers and can become widely distributed by flying, wind currents, vehicles and animals. Generally, however, flies are abundant in the immediate vicinity of their breeding site. Under certain conditions, they may migrate 1 to 4 miles, but are usually limited to one-half to 2 miles.

House flies feed by using sponging type mouthparts. As the fly moves about from one food source to another, it samples and eats its food by regurgitating liquid and dropping it on the food to liquify it. Light colored spots called fly specks are visible signs of this type of feeding. Darker fly specks associated with house flies are fecal spots.

The house fly's feeding and breeding habits along with its persistence for invading homes and feeding on human food enable the house fly to spread many intestinal diseases such as dysentery and diarrhea.

Resistance is a complex problem associated with chemical control of insects. Recognized some 50 years ago, it is not a new problem. Defined, resistance is the ability of an insect population to withstand exposure to insecticides, and this is acquired by breeding from insects that have survived previous exposures to an insecticide that did not wipe out the whole population. The surviving insects are resistant because either biochemical mechanisms (enzymes) enable them to quickly break down the insecticide or behavioristic adaptations enable them to somehow avoid the insecticide.

Stable Flies

The stable fly or dog fly is a blood-sucking fly which is of considerable importance to people, pets, agricultural animals, and the tourist industry in Florida. Stable flies primarily attack animals for a blood meal, but in the absence of an animal host will also bite man.

Adult stable flies can fly up to 70 miles from their breeding sites. The stable fly adult is similar to the house fly in size and color. The stable fly, however, has a long bayonet-like mouthpart for sucking blood. Unlike many other species of flies, both male and female stable flies suck blood.

The stable fly breeds all year in Florida although peak populations occur from August through September or October.

Stable fly bites are extremely painful to both man and animal. When hungry, stable flies are quite persistent and will continue to pursue a blood meal even after being swatted at several times. Although the bite is painful, there is little irritation after the bite, and few people exhibit an allergic reaction to stable fly bites.

The most practical and economical method for reducing stable fly populations is the elimination or proper management of breeding sources. It is important to remember that stable flies cannot develop in dry materials.

Stable flies breed in three principal types of material:

Flesh Flies

Flesh flies  are a scavenger fly species that usually feeds on carrion or meat scraps in garbage. They are medium- to large-sized flies and usually have 3 dark thoracic stripes and mottled abdomens. Many of the common species have a red tip on the abdomen.

Flesh flies retain their eggs within the body of the female until they are ready to hatch. The larvae are deposited directly onto the food the immature will be eating. The life cycle for the common species can be completed in 8 to 21 days.

The preferred breeding media around residences are decayed flesh, spoiling meat, and manure. Usually garbage can meat scraps and dog food left outside are abundant sources of flesh fly breeding. Flesh flies can breed in dead rodents and birds in attics or wall voids of houses.

Blow Flies and Bottle Flies

There are quite a few species of blow flies and bottle flies which are found in and around residences. The greenbottle, bluebottle, and bronzebottle flies are particularly abundant in Florida. In urban areas these flies may be more abundant than house flies.

The blow flies and bottle flies usually have a metallic blue or green color or both on the thorax and abdomen. These flies are strong fliers and range many miles from breeding places. They are abundant during the warm summer months.

Blow flies and bottle flies can breed on dead rodents and birds in attics or wall voids of houses. They usually breed in meat scraps, animal excrement, and decaying animal matter around houses. The adult flies are quite active inside and are strongly attracted to light. The mature larvae are often a problem when they migrate from breeding areas to pupate.

Blow flies usually lay eggs on dead animals or decaying meat. Garbage cans have been known to produce 30,000 blow flies in one week. The life cycle usually lasts 9-21 days from egg to adult.

Filter Flies or Moth Flies

Filter/moth flies, (drain flies), belong to the family of flies called moth flies. They are 1/16 to 1/18 in in length; light gray to tan in color. Their life cycle is 7 to 20 days. Adult flies have the body and wings covered with dense, long hairs. Moth/filter flies breed in decomposing organic material, such as moist plant litter, garbage, sewage, around kitchen or bathroom sinks and water traps in plumbing fixtures.

Soldier Flies

The soldier fly is a widespread pest which occasionally becomes a problem in homes. The adult is a large fly about 1 inch long with 2 large translucent areas on the abdomen. The fly behaves like a wasp and is similar in appearance to a mud-dauber wasp. The larvae prefer to feed on human or animal excrement although they have also been known to breed in honey bee colonies killed in walls of houses.

Most frequently the larvae are found in bathrooms migrating from the septic tank or sewer line. The presence of the maggot under such circumstances indicates the septic tank or sewage line is not working properly.

Vinegar (Fruit) Fly

Fruit flies are nuisance pests and contaminators of food. Fruit flies usually breed in fruit, dirty garbage containers, or slime in drains, feeding on yeasts that grow on organic matter.

Each adult lays about 500 eggs which hatch and the larvae mature to adults in 9-12 days. These flies are readily attracted to fruit, vegetables, and soda bottles and cans.

Eye Gnats

Eye gnats are small flies, shiny black about 1/6 inch in length. The adults are strongly attracted to moisture around the eyes and nose of people outdoors. In mid-summer large numbers of eye gnats persistently hover around the face causing considerable annoyance. Often eye gnats enter the homes through open doors or windows. They are strongly attracted to light and observed mainly on windows in large numbers.

Eye gnats breed in soil containing considerable organic matter, decaying vegetation, and animal excrement. The life cycle varies from 7-28 days depending on the temperature and moisture.

Hump-Backed Flies

Hump-backed flies are about 1/8 inch long with a small head and large thorax, causing the fly to have a hump-backed appearance.

Hump-backed flies breed in decaying vegetation, animal debris, garbage, and in ant and termite nests.

Dump Flies

Dump flies are about 1/4 inch long, black in color with a shiny thorax and abdomen.

Dump flies breed in garbage and fowl excrement. The larvae are predacious on larvae of other flies.

Secondary Screwworm Flies

Secondary screwworm flies are about 1/4 inch long, green in color, shiny abdomen and thorax with thorax marked lengthwise with three dark stripes. Their life cycle is 9 to 39 days.

They breed in dead tissue surrounding wounds in animals, fresh cut meats, and garbage.

Control of Filth Flies

Sanitation (* along with the use of a safe pest control device such as the Rid-Max Fly Trap) is still the best method of controlling filth flies in and around the home and on the farm. Flies seek breeding places where garbage, animal droppings, or vegetation residues accumulate. Locate and thoroughly clean such places. Dry, spread or somehow dispose of dog, cat, or other animal excrement. Do not let garbage accumulate in the open and make sure garbage cans have sound bottoms and tight fitting lids.

Good fitting screens on windows and doors are essential in preventing flies from entering homes and kitchens. In areas with high humidity screens last longer when made of aluminum, plastic, or fiberglass.

Control of eye gnats is difficult. It is often hard to destroy breeding sites over the many acres of land where eye gnats breed. For personal protection outdoors repellents may be applied to the skin. Indoors, space sprays will kill adults which are trapped in the house.

Descriptions of filth-breeding flies:

Footnotes

This document is ENY-222, one of a series of the Entomology and Nematology Departmennt, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: June 1991. Revised: March 2003. Please visit the EDIS Website at http://edis.ifas.ufl.edu.

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