University of Lausanne researchers led by Jessica Purcell tested the rafting strategies of F. selysi. To do so, they first had to address a few questions, like how long can a worker ant survive being submerged in water? And just how buoyant is an ant larva? These questions were handily answered by holding worker ants under water and by floating larvae in increasing concentrations of detergent. Fun for everyone.
Next, the scientists encouraged colonies of ants to build rafts by slowly flooding the platform they were living on. The ant rafts are built solely of ant bodies, they used no other construction materials. As the rafts were constructed, the researchers observed their building strategies.
If there were larvae or pupae (brood) available, the workers would put them in a pile and climb on top. If present, the queen would then take a lofty position on top of the workers and float away in relative ease and safety.
You can observe this in the following video, which is shot from underneath. Note how pillowy and comfortable the large yellow ant brood looks.
As odd as it seems to our sensibilities, floating away on a pile of babies gives everyone a higher chance of success. Worker ants have a 79% survival rate after being submerged for eight hours, but ant brood fare even better. In addition, ant larvae and pupae are significantly more buoyant than the adult workers. Putting the brood on the bottom means that the adults stay drier and have subsequently shorter post-rafting recovery times, which could be crucial if the colony has to quickly establish a beachhead at the new location.
For your viewing pleasure: an unsinkable raft of fire ants, which employ a similar raft building strategy. And you thought magnets were fun to play with.
Purcell, J., Avril, A., Jaffuel, G., Bates, S., & Chapuisat, M. (2014). Ant Brood Function as Life Preservers during Floods PLoS ONE, 9 (2) DOI: 10.1371/journal.pone.0089211.
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