While some flies are beneficial to humans as parasites of insect pests or as scavengers and many others are important as plant pollinators, flies are also known to be carriers of such serious diseases as cholera, typhoid, and dysentery. In most species of fly the body and padded feet are covered with bristling hairs and the tongue is coated with sticky glue. Under a powerful microscope, samples of the dust and dirt clinging to these hairs reveal bacteria that cause a wide variety of diseases.
Flies get the germs from garbage and sewage.
If they touch food later, it too may become contaminated. More than just annoying insects, some mosquitoes are responsible for transmitting diseases that can result in serious illness and even death. Mosquitoes were once viewed merely as a nuisance because of the itching and irritation that resulted from their bites. In the early 1900s, however, they were recognized as carriers of yellow fever, malaria, and other diseases. Bees are flying insects that are related to wasps, hornets, and ants.