halteres

Halteres are paired balancing organs of the true flies (order Diptera). They are modified hindwings reduced to small, knob-like structures that protrude behind the wings and are connected to the thorax by a slender stalk. In flight, halteres beat in synchrony with the wings and act as gyroscopic sensors.

The knob and its base house mechanoreceptors that detect deflection of the haltere as the body experiences angular movement. Sensory neurons convey this information rapidly to the thoracic nervous system, providing real-time data about rotation around the three body axes. The haltere input is integrated with visual cues from the eyes to adjust wingbeat timing, stroke amplitude, and steering, helping the insect maintain stability during rapid maneuvers and hovering.

Halteres are a defining feature of Diptera and contribute to the exceptional aerial control of many flies. They are not present in most other insects, which rely on different balance-sensing systems such as antennae-based or body mechanoreceptors. Halteres evolved from hindwings in the Dipteran lineage and remain critical for flight performance across diverse fly groups.