The house fly and other types of “filth flies” can become nuisance pests, but also are important for their potential to harm humans and animals. House flies, for example, can spread diseases such as food poisoning and dysentery. Flies, including stable flies and mosquitoes (which also are classified as flies, or Diptera), can inflict painful bites while feeding on the blood of humans and other animals, and some species transmit disease.
The habits of filth flies favor the spread of bacteria and other disease-causing organisms. Filth flies often feed and lay eggs on garbage, manure and carrion before contaminating human foods and food preparation surfaces by landing on them. When feeding, house flies regurgitate their stomach contents onto food to liquefy it before
ingesting it. They also contaminate food and surfaces by defecation.
The order Diptera is composed of the “true flies,” one of the largest groups of insects. Diptera means “two wings.” True flies have only two wings (one pair) instead of four wings (two pair) found in most other types of winged insects. All flies are attracted to moist organic material upon which they lay their eggs. This habit makes filth flies valuable as scavengers, but also brings them in contact with humans.
Filth flies can be divided into two groups, determined by their appearance and food preferences. Filth flies such as the house fly, blow flies and flesh flies, are relatively small, soft-bodied insects with large eyes and are strong fliers. Other filth flies, such as drain flies, fruit flies and phorid flies, are smaller with more delicate bodies and legs.