Collective transport up vertical surfaces in the weaver ant Oecophylla smaragdina
Andrew Taylor Burchill, Andrew Taylor Burchill , Chris Reid
School of Life Sciences, Arizona State University, USA; School of Life Sciences, Arizona State University, USA ; Department of Biological Sciences, Macquarie University, Australia
Humans aside, ants are the only group of animals that regularly exhibit cooperative transport. The retrieval of large food objects by multiple individuals has independently evolved in many genera; this transport allows colonies to secure otherwise contested resources. Although there is large variation in the collective behaviors used during transport, most research effort has focused on items carried across horizontal surfaces or shallow inclines. However, in species such as the Australian weaver ant Oecophylla smaragdina, prey are often collectively carried over the ground and up sheer vertical surfaces such as tree trunks. Yet vertical transportation remains virtually unstudied. Although humans may initially think these two types of transport require different organizational modalities, this remains to be seen in ants. Using weaver ants, we first test which proximate cues—such as the mass or volume of a food source—are used by the ants to recruit nestmates needed for vertical and horizontal transport. We then investigate whether the information governing the ants’ coordination and performance is qualitatively different when gravity acts parallel to the direction of motion instead of perpendicular. This is achieved through monitoring collective transportation up a variety of inclines and substrates. By repeatedly recording the relative orientation and number of ants involved, we can suggest consistent behavioral rules.