For the keeping the Body steady and upright in Flight, it generally holds true, (if I mistake not,) that all bipennated Insects have Poisses joyn’d to the Body, under the hinder Part of their Wings; but such as have four Wings, or Wings with Elytra, none. If one of the Poisses, or one of the lesser auxiliary Wings be cut off, the Insect will fly as if one Side overbalanced the other, until it falleth on the Ground; so if both be cut off, they will fly aukwardly, and unsteadily, manifesting the Defect of some necessary part. These Poisses, or Pointells are, for the most Part little Balls, set at the Top of a slender stalk, which they can move every way at pleasure. In some they stand alone, in others, (as in the whole Flesh-Fly Tribe,) they have little Covers or Shields, under which they lie and move. The Use, no doubt of these Poisses and secondary lesser Wings is to poise the Body, and to obviate all the Vacillations thereof in Flight; serving to the Insect as the long Pole, laden at the Ends with Lead, doth the Ropedancer.
Derham’s writing indicates that he had not only observed the halteres of flies but had removed them to determine the effect. Halteres somewhat resemble the balancing poles of the ropedancer, but on a smaller scale, which led Derham to conclude that halteres worked in a similar manner. This impression persisted for over 200 years when additional thoughtful experiments were performed that proved otherwise..