Gliding hexapods and the origins of insect aerial behaviour.

Directed aerial descent (i.e. gliding and manoeuvring) may be an important stage in the evolution of winged flight. Although hypothesized to occur in ancestrally wingless insects, such behaviour is unexplored in extant basal hexapods, but has recently been described in arboreal ants. Here we show that tropical arboreal bristletails (Archaeognatha) direct their horizontal trajectories to tree trunks in approximately 90 per cent of falls. Experimental manipulation of the median caudal filament significantly reduced both success rate (per cent of individuals landing on a tree trunk) and performance (glide index) versus controls. The existence of aerial control in the ancestrally wingless bristletails, and its habitat association with an arboreal lifestyle, are consistent with the hypothesis of a terrestrial origin for winged flight in insects.