The insect order containing houseflies, mosquitoes and gnats is Diptera.
Diptera means “two wings,” a reference to the single functional pair of wings carried by adult members. Their hindwings have evolved into tiny balancing organs called halteres, which sense body rotation and help flies perform agile, controlled flight. This feature distinguishes true flies from insects such as butterflies and dragonflies, despite those names ending in “fly.”
Diptera includes more than 150,000 formally described species, among them houseflies, fruit flies, blowflies, midges, black flies and crane flies. Most undergo complete metamorphosis, with egg, larva, pupa and adult stages. Mosquito larvae are commonly aquatic, while housefly larvae are maggots that develop in decaying organic material. The group matters to people both positively and negatively: flies pollinate plants and recycle nutrients, while some mosquitoes and other dipterans transmit disease.