Last time we discussed how certain species of ants can swim. Even if they can't swim, some species are able to withstand temporary floods by grouping together to form living rafts to float on the water.
Although there has been a rash of papers about the ability of fire ants to form rafts, Jessica Purcell, assistant professor of entomology at The University of California, Riverside, has been studying the ability to float by Alpine silver ants, Forica selysi.
After marking some of the worker ants, the researchers subjected the ants to flooding. They discovered that when the same ants were subjected to flooding a second time, many of them assumed the same positions in the rafts. Rather than coming together randomly, as might be expected during a flooding crisis, the ants were apparently assembling in a somewhat organized fashion.
This video shows the experimental protocol. Note: You probably will want to turn down your computer's sound or hit mute before you click on the play button.
Based solely on this video, I'm going to suggest that painted ants tend to be towards the outside of the raft. Is it possible that damaged ants (painted ants) can assess their health and position themselves at the rim? Of course, that may have happened at random, too. What do you think?
All ants on deck, EurekAlert, AAAS
Purcell J, Avril A, Jaffuel G, Bates S, Chapuisat M (2014) Ant Brood Function as Life Preservers during Floods. PLoS ONE 9(2): e89211. doi:10.1371/journal.pone.0089211