Ants use their babies as life rafts during floods, according to a new study. This unusual behavior was observed in ants living in flood plains. The behavior may have evolved from ants living in the rainforest of Brazil long ago. 

When large colonies of ants are caught in water, the insects create rafts from their own bodies. By linking together into a flat circle, they are able to trap air beneath the group. These living structures are usually three to four ants thick, containing a total of 500 to 8,000 individuals under laboratory conditions. In the wild, these rafts contain up to 100,000 ants. 

Researchers from the University of Lausanne in Switzerland studied the position of young ants in the floating pancakes. Among their findings, they were found to line the bottoms of the makeshift rafts with their own highly buoyant young. This exposes the brood to water, and the fish that may eat the tiny insects. 

"By causing groups of ants to raft in the laboratory, we observe that workers are distributed throughout the raft, queens are always in the center, and 100% of brood items are placed on the base. Through a series of experiments, we show that workers and brood are extremely resistant to submersion," the researchers wrote in a journal article accompanying the study.

The research was lead by Jessica Purcell, an ecologist at the University of Lausanne, Switzerland. Her team determined keeping young ants on the bottom of the raft serves several purposes. The practice helps preserve the integrity of the colony, takes advantage of the natural buoyancy of brood ants, and allows adult worker ants to recover more quickly. Most of the young insects survive the experience. In experiments, the group was able to show 79 percent of brood ants survived eight hours under water. 

Not all ants are happy with their position on these rafts, however. Purcell's team found some individuals were forced to take positions in the water, or on the edge of rafts.

"We find that ants can considerably enhance their water repellency by linking their bodies together, a process analogous to the weaving of a waterproof fabric. We present a model for the rate of raft construction based on observations of ant trajectories atop the raft. Central to the construction process is the trapping of ants at the raft edge by their neighbors, suggesting that some "cooperative" behaviors may rely upon coercion," Purcell and her team wrote

Research on the use of baby ants as life rafts was detailed in the online journal Plos One.

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