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How do true flies differ from dragonflies, caddisflies, and mayflies?

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Housefly — Diptera An adult housefly (*Musca domestica*) on a doughnut

True flies (order Diptera) are distinguished from other insects commonly called "flies"—such as dragonflies, caddisflies, and mayflies—primarily by their unique wing structure.12

While many insects possess two pairs of wings, true flies are characterized by having only one pair of functional forewings used for flight. Their second pair of wings is reduced to small, knoblike structures called halteres. These halteres act as gyroscopes, vibrating in time with the wings to provide balance and allow the insect to correct its flight attitude during yawing, rolling, or pitching.132

In contrast:
* Dragonflies possess two pairs of intricately veined, membranous wings.4
* Caddisflies and mayflies also differ from true flies in their wing structure, as they do not possess the specialized halteres found in Diptera.32

These anatomical differences serve as the primary taxonomic features used by entomologists to distinguish true flies from other winged insects.13