1. University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas 77555, USA
2. University of Florida Medical Entomology Laboratory, 200 9th Street SE, Vero Beach, Florida 32962, USA
3. Department of Integrative Biology, University of California, Berkeley, California 94720, USA
4. Smithsonian Tropical Research Institute, PO Box 2072, Balboa, Republic of Panama
5. Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019, USA

Correspondence to: Michael Kaspari^4,5 Correspondence and requests for materials should be addressed to M.K. (Email: mkaspari@ou.edu).

Abstract

Numerous non-flying arboreal vertebrates use controlled descent (either parachuting or gliding sensu stricto ^{1, 2}) to avoid predation or to locate resources^{3, 4, 5, 6, 7}, and directional control during a jump or fall is thought to be an important stage in the evolution of flight^{3, 8, 9}. 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.

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