Noun
The word is derived from halter
Balancers; the rudimentary hind wings of Diptera.
Source: Webster's dictionaryOnly flies have true halteres. In fact, the scientific term for flies, 'diptera,' means 'two wings.' Most insects, including bees, have two pairs of wings for a total of four. In flies, the hindwing pairs have been transformed through evolution into the halteres. Michael Dickinson
An extreme example of this trait is in the family Syrphidae (hoverflies), where the bulb of the haltere is positioned nearly perpendicular to the stalk. citation Flies typically hold their halteres at a 90 degree offset. Source: Internet
Another structure in the class insecta also exists whose primary function is not the same as halteres, but that additionally serves a similar balancing function. Source: Internet
Brachyceran flies (short-antennaed) oscillate their halteres almost exactly opposite their wings (180 degrees). Source: Internet
Flesh flies are among those that oscillate their halteres while walking, and also perform more poorly at certain walking tasks when their halteres are removed. Source: Internet
Because the halteres are set at different angles (90 degree offset), they also beat along two separate horizontal and vertical axes. Source: Internet