Flooded Ants Build a Raft to Save Themselves and Queen

When faced with a flood, worker ants link bodies and use the brood's buoyancy in order to save themselves and protect the queen, according to a new study.

Social animals, such as ants, have often been observed to work together to enhance the survival of the group when put in a dangerous situation. Ants living in known flood plains are known to link together and create a raft during floods, but little is understood about the composition of the rafts.

In a study published in PLOS One, Jessica Purcell from University of Lausanne, Switzerland and her colleagues collected ants from a flood plain in Switzerland and brought them back to the lab for testing. The researchers flooded populations of the ants that consisted of different combinations of worker ants, queens and brood, which are larvae and pupae. While the ants scrabbled to prepare for the laboratory made flood, the team observed where the three types of ants were positioned in the raft.

They were also able to understand the buoyancy of the types of ants as well as the ability for worker ants and brood to recover after being submerged.

During the experiment, researchers observed that worker ants and brood were "extremely resistant to submersion," according to a press release announcing the findings. The queen, as the most valuable ant in the nest, was placed in the center of the raft by the worker ants. The workers then put the brood at the base, to capitalize on their buoyancy, while using their own ability to recover from submersion in order to minimize injury and death.

Occupying the base of the raft was not a death sentence, as scientists found that the worker ants and brood exhibited high survival rates. The brood may have also been placed at the base to help keep the nest together during the flood, according to the team.

Purcell added, "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. Further experiments revealed that the brood are the most buoyant members of the society and that rafting does not decrease their survival; thus, this configuration benefits the group at minimal cost."