Directed aerial descent in canopy ants

Numerous non-flying arboreal vertebrates use controlled descent (either parachuting or gliding sensu stricto ) to avoid predation or to locate resources, and directional control during a jump or fall is thought to be an important stage in the evolution of flight. Here we show that workers of the neotropical ant Cephalotes atratus L. (Hymenoptera: Formicidae) use directed aerial descent to return to their home tree trunk with >80% success during a fall. Videotaped falls reveal that C. atratus workers descend abdomen-first through steep glide trajectories at relatively high velocities; a field experiment shows that falling ants use visual cues to locate tree trunks before they hit the forest floor. Smaller workers of C. atratus, and smaller species of Cephalotes more generally, regain contact with their associated tree trunk over shorter vertical distances than do larger workers. Surveys of common arboreal ants suggest that directed descent occurs in most species of the tribe Cephalotini and arboreal Pseudomyrmecinae, but not in arboreal ponerimorphs or Dolichoderinae. This is the first study to document the mechanics and ecological relevance of this form of locomotion in the Earth's most diverse lineage, the insects.