Prey escorting behavior and possible convergent evolution of foraging recruitment mechanisms in an invasive ant

Abstract

The longhorn crazy ant Paratrechina longicornis is a pest ant species with worldwide distribution. It tends honeydew-producing Hemiptera to obtain carbohydrates and is also an effective predator and scavenger. What strategies does P. longicornis use to aid in hunting and scavenging? Our results show that as well as long-term recruitment to stable food sources, this species uses specialized short-term recruitment pheromones to recruit nest mates to assist in the exploitation of large food items. By mass, 88% of externally carried food was retrieved cooperatively. Recruitment to large items is via a pheromone trail laid by the discovering ant. This trail is initially followed with few errors by naive recruits (82% correct choices at a T-bifurcation) but decays very rapidly (within 6 min). We also show that food-discovering ants can recruit nearby nest mates to a large food item without returning to the nest. These properties of the recruitment system are strikingly similar to 2 unrelated ant species, which also specialize in cooperative retrieval of large food items, suggesting convergent evolution. Lastly, we describe a novel “escort” behavior in which additional workers accompany a transported item but do not necessarily assist in carrying it. Both local recruitment and escorting are much more pronounced (3 and 4 times greater, respectively) when handling live prey. When an “escort” is present, live prey presented to the ants is 50% more likely to be captured and is captured 4 times sooner and 50% closer to the release point.