Why do Acromyrmex nests have thatched entrance structures? Evidence for use as a visual homing cue

Abstract

Ants can learn to recognize and memorize visual aspects around their nests for visual guidance. Thatched entrance structures are a trademark of the genus Acromyrmex. We hypothesized that the thatched structure serves as a visual cue for Acromyrmex balzani workers while homing. Fifteen colonies located in a pasture area were used to test whether thatched structure displacement and odor removal alter the behavior of returning ants. Nests were divided into three groups: (1) control observations, (2) displaced thatched structure, which we moved 30 cm to the right side of the nest entrance and (3) displaced and odorless thatched structure. Route direction and time spent by five workers to reach the nest entrance were measured. For manipulated nests, workers were disoriented and took longer to reach the nest entrance relative to control colonies. These results are in accordance with the idea that environmental alterations may influence ant navigational abilities and suggest that A. balzani workers can perceive recent modifications around the nest while homing. The observed disorientation by workers in response to the displaced and odorless thatched entrance suggests that it can act as visual cue to homing behavior of A. balzani. Future researches manipulating thatched structure and chemical cues around the nest entrance may generate knowledge about the importance of both types of cue for navigation in ants.