Re: Why do a group of stranded ants cluster tightly together?

Dear David,

I am not entirely certain that I know what the phenomenon you are describing is. I suspect that it is either related to chemistry or ecology. If the ants are sticking together simply because they are floating in water, then the answer comes from understanding their external chemistry. Insects are protected from dehydration by a cuticle composed of layers of proteins and chitin. This cuticle is hydrophobic which means that it repels water, thereby keeping liquids from passing through it. If surrounded by water, hydrophobic material tends to clump together, like beads of oil on the surface of water in a dirty pot before you add soap to wash it.

To see a scanning electron microscopic picture of insect cuticle, see the University of Miami Biology Department's webpage.

So the ants may be floating together in clumps because their cuticles are hydrophobic.

Or, if the ants are floating together because they want to float together, then the answer comes from understanding their behavior. Again, it is difficult for me to know exactly what the ants you see are doing. If they are clinging to one another because they are desperate to cling to anything solid, then the behavior is probably done to prevent the ants from getting lost. If an ant is searching for food near its colony, and a flood comes, the ant will want to cling to something solid (such as a tree) so that when the water leaves, it will be able to find its nest again.

If the ants are clinging to one another because they want to be with other ants from their colony, then the behavior is called aggregation. Insects aggregate for many reasons, many of which are well described (with citations) by Mark Sisterson, a student from Colorado State University's department of entomology. In his paper, Mark does not describe aggregations of social insects (such as ants). Social insects aggregate because they work together to maintain their colony. Many biologists describe social insect colonies as superorganisms with individual insects as parts of the larger superorganism colony. A great explanation of why social insects act as part of a superorganism is found on Rice University's Department of Ecology and Evolutionary Biology's website.

If an ant colony became flooded, the ants that floated to the surface of the water might want to stick together so that once the flood was over, the survivors could work together to rebuild their colony's nest. It is the cooperation of all the ants that makes the colony successful. Fire ant colonies are famous for floating together on the top of water during floods. The Texas A&M University maintains a website about fire ants, which contains this fantastic photograph of fireants floating together during a flood.

So, in summary, there are several possible reasons why the ants you see are floating together in water. It could be that the hydrophobic cuticle of the ants draws them together, it could be that the ants are clinging to any solid material in order to prevent getting lost in a flood, or it could be a form of aggregation, in which the ants are trying to stay together so that when the flooding is over, they can work together to repair their colony.

I hope that this information has been helpful to you (or at the very least interesting)! I hope that if you have any further questions, you will ask us again!


Sincerely yours,

John Carlson