There are 5 types of flies that commonly infest schools: Houseflies (Musca domestica), Blow flies (in the family Calliphoridae), Cluster flies (Pollenia rudis - also in the family Calliphoridae), Moth flies (in the family Psychodidae), and Fruit flies (several species of Drosophila in the family Phoridae). Fly infestations in schools and childcare centers are a problem not only in that people find them annoying, but also because they pose a very real problem for humans through the spread of bacterial infections and disease.

All flies are in the order Diptera, meaning they have only one pair of wings. This makes it easy to tell flies apart from other flying insects, which have two pairs. Flies are scavengers, and the ones found in schools are liquid feeders, with mouthparts appropriate to sucking and lapping. Their most important food source is decaying material, and they are very important to the process of decomposition, recycling nutrients back through the ecosystem. Overall, flies help to keep facilities cleaner. Nonetheless, although flies play a necessary part in nutrient cycling, when infesting buildings, they may pose a threat to human health, as they carry disease-causing germs from food source to food source, including human food. For this reason, flies are controlled.

The primary problem in schools is the Housefly. Attracted to wet, decaying organic matter, such as food material, plant matter, feces, or dead animals, the female will lay her eggs here 4-8 days after mating. Over the course of a day, the female will lay 100-150 eggs in various locations. Larvae, called "maggots," emerge 12-24 hours after the eggs were laid. After the maggots have eaten enough and molted three times, their skin hardens and darkens, and they become a "pupa." Inside these casings, the body structure changes radically, and after a few days the adult fly emerges from within. The change from egg to adult may be completed in as little as 8 days if temperatures are warm, or may take weeks if temperatures are cool. The new females can mate and lay eggs 3-10 days after emerging themselves. Three days after a Housefly lays eggs, it will mate again. The average female will produce 2-6 batches of eggs during her lifetime. Houseflies live, on average, 21 days, with the exception of those that diapause. During winter months, the egg, maggot, or pupal stage, will enter into a state of rest, called "diapause," similar to hibernation until the following spring when the life cycle can be completed. On the feet of houseflies are tiny pads covered with hair which ooze a sticky liquid. These sticky hairs not only enable them to cling to any surface, but also are responsible for bacteria sticking to the feet. This, and the habit of regurgitating stomach contents to dissolve food, means that Houseflies may transmit a huge range of bacterial, viral, and protozoal infections. They spread bacteria responsible for diarrhea, dysentery, and food poisoning, and are known to have spread Typhoid fever. They also carry cholera and intestinal worms.

Blow flies, like Houseflies, will live on feces, meat scraps in garbage, wet mixed garbage, and dead animals. Similarly, they can also contaminate food. These flies are about a quarter-inch long and their thorax and abdomens are shiny black, metallic green, or bronze, or they have a dull-colored thorax, with a metallic blue abdomen. In some Blow flies, the eggs hatch while still within the female, and she will deposit live larvae, preferably on raw meat and sometimes on festering cuts and sores where the larvae will feed on the living tissue. If these larvae are accidentally eaten, the hardy maggots continue to grow, irritating the stomach and intestine, causing nausea, vomiting, and severe diarrhea.

Cluster flies are larger than the previous flies, and seem sluggish in comparison. They can be identified by yellow hairs on the thorax. The larvae develop as parasites in the bodies of earthworms, and the adults emerge in late summer and early fall. These adult cluster flies seek protected places to spend the winter, and will frequently end up in the walls and ceilings of buildings. They enter through small openings, such as wire penetrations, cracks around windows, openings around the roof, etc. These flies will come out of hiding in the spring or on warm winter days, and cluster around windows in an attempt to enter.

Moth flies are about an eighth-inch long, hold their wings over their body at an angle that is roof-like, and have long drooping antennae. The larvae live in the gelatinous material in drains, sink traps, and sewers. If drains are not cleaned often, they will continue to appear and spread within the building.

Fruit flies are very small, have red eyes, a yellowish to brown thorax, and yellow bands on the abdomen. Although short-lived (two weeks maximum), females produce about 100 eggs at a time. They prefer to lay their eggs in crack in the peels of fruits or vegetables. From the time the eggs are laid to the emergence of adult fruit flies, takes about a week. They are attracted to the odor of fermentation from ripe fruit and vegetables, or fermenting water from refrigerators, humidifiers, drains, sour mops or rags, or from anything else that will ferment.

In the effort to control flies, concentration should be placed on their exclusion from the building and eliminating breeding sites. The most common entry point into the school is usually an open door or an unscreened window. If suddenly there seems to be a fly problem where earlier there was not one, look for a door or window which may be propped open. In general, seal screens, windows, doors, ventilators, eaves, etc. When replacing screens, use screen with a small mesh to be sure to exclude smaller fruit and drain flies. Be sure to dispose of all fly-infested material both inside and outside the school building. Clean up any food spills immediately. Garbage cans should have tight-fitting lids, and wet garbage should be wrapped and put in plastic garbage bags. If the garbage receptacle is too full for the lid to fit tightly, then the garbage should be removed immediately. Be sure to clean garbage cans, dumpsters, and drains frequently. Do not allow food items to sit out for long periods of time. Store food items in air-tight containers or a refrigerator. When dealing with a small fly infestation, the best method of control is a simple fly swatter. Every classroom should have access to one. If these measures are followed and a significant fly problem persists, contact the IPM Coordinator to discern and treat the problem.

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