Ants build rafts to escape flood, protect queen

During floods worker ants link their bodies and use the brood's buoyancy to build rafts University of Lausanne

When facing a flood, ants build rafts and use the buoyancy of the brood and the recovery ability of workers to protect their queen and minimise injury and death, scientists at the University of Lausanne have shown.

During flooding, worker ants link bodies and protect the most vulnerable and valuable nest mate, the queen, by placing her in the centre of the raft, according to research released by scientific publisher PLOS ONE on Wednesday.

When put in harm’s way, social animals are often able to work together to enhance the survival and welfare of the group. Ants living on flood plains are known to link together to create rafts during floods, but less is known about the composition, shape and social structure of these rafts.

“We expected that individuals submerged on the base of the raft would face the highest cost, so we were astonished to see the ants systematically place the youngest colony members in that positions,” lead researcher Jessica Purcell explained.

“The brood are the most buoyant members of the society and rafting does not decrease their survival; thus, this configuration benefits the group at minimal cost.”

Purcell collected ants from a flood plain in Switzerland and brought them back to the lab so she could induce flooding in ant populations containing worker ants, queens, developing larvae and pupae. During the flooding, she observed where the workers, brood and queens were positioned in the raft.

The Lausanne researchers showed that both workers and brood exhibited high survival rates after they rafted, which suggests that occupying the base of the raft is not as deadly as scientists expected. Placing the brood at the base of the raft may also aid in keeping the nest together during the flood.

The Swiss National Science Foundation supported the research at the University of Lausanne with a grant.