Tandem running, a new mystery behind ant lines

 Lining up ants are a usual sight that has amazed everybody during their childhood days. While changing environmental conditions and increased competition trigger nest relocation among ants, how they carry out the logistics of relocating hundreds of members and resources to the new nest is very interesting.

It is widely known that the ants keep the line with the help of trails marked by chemicals from their body called pheromones to reach the destination. However, a new research has revealed another method, called tandem running found among Diacamma indicum ants -a species found in Sri Lanka and India - being used in colony relocation.

Tandem run is a reason why you find ants doing something like shaking hands with each other. To initiate a tandem run, a leader ant, often an adult, will repeatedly make antenna contact with a potential follower. Then turning around by 180 degrees, the tandem leader will provide her abdomen to the follower. The follower will then touch the abdomen of the leader with the antennae signaling that she is ready for the move. Thus the pair moves to the nest all the while keeping continuous physical contact.

You believe it or not, ant colonies were found taking almost same time to relocate to new nests in this way, no matter what distance they cover. The study found one ant colony which moved to a shorter distance destination taking as much time as another which traveled to a distance six times farther. To adjust this, during long distance relocations, more worker ants took the role of leaders initiating tandem run which in effect made the relocation faster for the whole colony.

It was also observed that D. indicum ants allow only the broods and males to be followers, and they never swap leaders and followers during a tandem run.

Interestingly, D. indicum ants don’t have an egg-laying queen, unlike many other ant species. The egg-laying role is taken by a worker ant called gamer-gate. During relocation, the gamer-gate was either tandem run or self explored to the new nest without company of retinue, unlike the queen ants in other species.