Some flying insects have two wings, whereas others have four. The common housefly, which possesses two wings, makes use of the vestigial hindwing (the pendulum-shaped haltere) as a source of mechanosensory input to the neural centers that support stable flight. Sane et al. have asked whether moths, which have four wings, possess a similar kind of flight control mechanism. Instead, the antennae appear to serve a haltere-like function by providing mechanosensory input through hairs or bristles located at their base, whose deflections are translated into afferent neural signals.