Predation on large millipedes and self-assembling chains in Leptogenys ants from Cambodia

Abstract

Various ants can link their bodies in chains or other structures, a striking example of cooperation. Chain behavior in Leptogenys sp. functions for the collective transport of large millipedes. This undescribed Leptogenys species is a swarm raider with a small range of prey: millipedes belonging to four orders (Polydesmida, Spirostreptida, Spirobolida, Sphaerotheriida), and occasional earthworms. Small prey were carried individually or dragged by a few ants, while chains made it possible to move millipedes weighing up to 16.4 g. Chains (either linear or branched) changed according to obstacles along the way to the nests. Between 2 and 52 workers were observed to drag single prey items, with only a few ants directly grasping the prey. One 15-cm-long millipede was captured rodeo-style after being encircled by 25–30 ants. As it uncurled from a defensive coil, the ants held back except one that tried to sting between its legs. The millipede started thrashing about which caused many ants to attempt stinging. While four other ponerine genera hunt millipedes solitarily, chains have never been reported.