Halteres

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Crane fly, with a pair of halteres visible below the wings as appendages, about as long as the animal's antennae, with knobs on the end

This article concerns insect anatomy. For halteres as used in ancient sports, see Halteres (ancient Greece)

Halteres (IPA pronunciation [hæl'tɪəriːz]; singular halter or haltere), also known as balancers or poisers, are small knobbed structures found as a pair in some two-winged insects; they are flapped rapidly to maintain stability when flying.

Halteres are homologous to, and evolved from, insect wings. The ancestral insect species had two pairs of wings (like most flying insect species today). In the Strepsiptera the forewings changed into halteres, while in the Diptera (flies, mosquitoes and gnats) the hindwings evolved into halteres.

Halteres operate as vibrating structure gyroscopes: the vibrating halteres tend to maintain their plane of vibration, and if the body of the insect turns or changes direction in flight, a bending strain develops which the animal detects with sensory organs known as campaniform sensilla located at the base of the halteres.

Halteres thus act as a balancing and guidance system, helping flies to perform their fast aerial acrobatics. They play an important role in stabilising the gaze of these insects during flight and also provide rapid feedback to wing-steering muscles to stabilise aerodynamic force moments. They are the equivalent of an aircraft's attitude indicator.