Halteres
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Halteres (singular halter or haltere) are small knobbed structures found as a pair in some two-winged insects; they are flapped to maintain stability when flying.
Halteres are homologous to and evolved from 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 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 oldest known type of vibrating structure gyroscope, providing flying insects with the equivalent of an aircraft attitude indicator.
The term halteres comes from the Greek word for dumbbells. In ancient Greek sports, halteres were used as lifting weights, and also as weights in their version of the long jump, which was probably a set of three jumps. Halteres were held in both hands to allow an athlete to jump a greater distance; they may have been dropped after the first or second jump. According to archaeological evidence, the athlete would swing the weights backwards and forwards just before take-off, thrust them forwards during take-off, and swing them backwards just before releasing them and landing.
Halteres were made of stone or metal, and weighed between two and nine kilograms. Writing in Nature, biophysicist Alberto E. Minetti of Manchester Metropolitan University calculates that halteres added about 17cm to a 3m long jump.
(ref: Nature 420, 141 - 142 (14 November 2002); doi:10.1038/420141a)de:Haltere