The ability to fly has enabled insects to evade predators, disperse, and
occupy diverse niches leading to their remarkable success. Most flying
insects have undergone miniaturization. Miniaturization or a reduction in
body size implies reduced wing span which results in reduced aerodynamic
forces. To overcome the reduced lift, flies (order Diptera) flap their
wings at very high frequencies, often exceeding 100Hz. These rapid wing
beats are powered by specialized myogenic muscles. Their fast and exquisite
flight maneuvers are controlled by rapid feedback from halteres; modified
hind wings that have evolved into mechanosensory organs. Halteres also
oscillate at wing beat frequencies but at precise phase relationship to the
wings. The two contralateral wings also oscillate precisely in-phase with
each other. Flies must maintain precise phase coordination between wings
and halteres for stable flight. This coordination occurs at rates that are
often difficult to achieve via active neural control. Our results show that
this rapid and yet coordination of wing and haltere motion is achieved by
passive, mechanical connections within the fly thorax instead of being
under active neural control. Coupled by mechanical linkages, wings and
halteres act as coupled oscillators. This mechanical coupling ensures
robust coordination even if there are slight differences in the natural
frequencies of wings and halteres due to developmental errors or
environmental damage for e.g. in flies with torn wings often seen in the
wild. In addition to the passive, rapid coordination flies use an actively
controlled clutch and gear box under each wing base which allows
independent control of individual wing motion despite being mechanically
connected. Passive mechanical coupling might be a general mechanism that
enables rapid coordination in various miniaturized insects like bees (order
Hymenoptera) and beetles (order Coleoptera).