The role of visual cues in directed aerial descent of Cephalotes atratus workers (Hymenoptera: Formicidae)

Animals often depend on properties of reflected light (e.g. color, brightness) to locate resources. We compared reflectance properties of tree trunks with surrounding vegetation, and examined how differences in reflectance profiles of surrogate tree trunks (red, yellow, green, blue, black, gray, dark gray and white sheets) affected the directed aerial descent of worker Cephalotes atratus (L.) ants. Across the visual spectrum, tree trunk reflectance was 2-10 times higher than the surrounding foliage and differed among trees. In two separate experiments, one with colored sheets and one with black, white and gray sheets, nearly half (42% and 47%, respectively) of falling ants directed their descent to a bright white sheet when given a choice of target colors or shades of gray. When colored and gray sheets were presented individually, landing frequencies were lower than expected for all except white sheets. Glide performance was highly variable, but there was a tendency for higher glide indices to be associated with the white sheet relative to the green sheet. We conclude that visually mediated aerial behavior in falling canopy ants is strongly influenced by reflectance properties of the target object, specifically brightness, and correlates with preferred natural targets of tree trunks.