Rafting: Merge or Die Fighting

Fire ant raft
Photo: PNAS

Native fire ant areas are subject to flooding. Fire ant colonies form rafts to float on the water and survive until they can reach dry land. Cassill and colleagues* studied the behavior of Solenopsis invicta fire ants rafting on water when two rafts meet. If the ants are from the same colony or from a nearby colony, the ants at the point of contact form links with the other raft. Over time, the ants shift their position so the two rafts transition from a “figure 8” (with one point of contact between the rafts) into a single circle.

Rafts from colonies separated by a distance of 45 miles did not cooperate and merge. Instead, the workers fought to the death. Workers engaged in fighting were unable to remain afloat, sunk and drowned. Cooperation or accommodation are clearly better strategies for rafting than fighting.

Workers from neighboring colonies are more likely to have encounters and can evolve behaviors that attenuate aggression. Behaviors that do not result in the death of both workers when neighboring ant workers meet would benefit both colonies. Aggression can be attenuated in these encounters for mutual benefit. This is especially true of encounters during rafting. The ability of rafts from neighboring colonies to attenuate fighting and facilitate merging gives both colonies a better chance of survival. Even in the world of ants the consequences of fighting can have far more negative outcomes than cooperation or accommodation.

Deby Lee Cassill · Alexander Casella · Jaeson Clayborn · Matthew Perry · Michael Lagarde. 2015. What can ants tell us about collective behavior during a natural catastrophe? J Bioecon
DOI 10.1007/s10818-015-9195-2