
Flies are insects in the order Diptera, which means “two wings” in Greek. They have one pair of wings for flying, while their back wings have changed into halteres, which help them sense movement and perform agile flying. Diptera includes over 150,000 species, such as horseflies, craneflies, hoverflies, and mosquitoes.
Flies have a flexible head with large compound eyes and mouthparts for piercing and sucking (like mosquitoes and black flies) or for lapping and sucking in other types. Their wing structure allows for great maneuverability in the air, and they can cling to smooth surfaces using claws and pads on their feet. Flies undergo complete metamorphosis: they lay eggs on food sources for the larvae, which do not have true limbs and grow inside a safe environment, often within their food. Some species give birth to live larvae instead of laying eggs, placing them on carrion, dung, or open wounds. The pupae are hard capsules from which the adult flies emerge when they are ready. Most adult flies have short lifespans.
Diptera is an important insect order for the environment and humans. Flies help pollinate plants, ranking second only to bees. They may have been some of the first pollinators of early plants. Researchers use fruit flies as model organisms in scientific studies. However, mosquitoes can spread diseases like malaria, dengue fever, and yellow fever, while houseflies spread foodborne illnesses. In many places, flies can be a nuisance, buzzing around and biting. Larger flies, like tsetse flies and screwworms, can harm cattle economically. Maggot larvae, known as gentles, are used for fishing bait and as food for carnivorous animals. They also help with cleaning wounds in medicine.