Smithsonian researchers have documented for the first time behavior reminiscent of "cleaner fish" in the sea: small ants climb onto large harvester ants and clean their jaws as well
In the deserts of southeastern Arizona, tiny ants have been recorded cleaning much larger ants. The unusual behavior was observed near the nests of small ants of the genus Dorymyrmex, sometimes called cone ants. Large harvester ants of the species Pogonomyrmex barbatus would come to the entrances of their nests, stand motionless, and open their serrated jaws. Instead of attacking, the tiny ants would climb on them and begin to gently lick and bite tiny particles off their bodies, and even out of their open jaws.
The behavior was described in a study published in the journal Ecology and Evolution. The observation was documented by entomologist Mark Moffett, a research associate at the Smithsonian's National Museum of Natural History. He said it is an insect equivalent of cleaner fish in the ocean, which remove parasites and dirt from the bodies of larger fish, sometimes even from the mouths of potential predators.
Moffett observed the phenomenon at a research station in the Chirikawa Mountains of Arizona. At first, he thought it was an aggressive event, since ants of different species tend to fight each other. But the larger ants made no attempt to escape or attack. Instead, they seemed to be seeking the attention of the smaller ants and allowing them to clean their bodies.
Cleaning sessions – between 15 seconds but sometimes more than five minutes
Over several days, Moffett recorded at least 90 such encounters. Typically, a harvester ant would approach a nest of cone ants, stand upright, and open its jaws. Within about a minute, one small ant, and sometimes up to five ants, would emerge and mount the body of the large ant. The cleaning sessions sometimes lasted less than 15 seconds, but in other cases more than five minutes.
Researchers are still not sure what each party gains from this relationship. It is possible that the smaller ants feed on energy-rich particles that they remove from the bodies of the harvester ants, perhaps seed scraps that the larger ones collect. The fact that they ignored dead ants placed near their nests strengthens the possibility that this is an active interaction with live ants, and not just a matter of eating scraps.
Harvester ants may also benefit from the service. Ants clean each other to remove dirt, spores, and parasites, but the smaller ants may reach areas that are difficult for larger ants to clean themselves. Future studies could examine whether cleaning reduces infections, alters the ants' microbiome, or provides a survival advantage to one party.
The finding highlights how complex relationships in nature can be hidden in small, almost invisible behaviors. Even among relatively well-known and well-studied insects, patient observation in the field can reveal previously undocumented collaborations.
To the article on the Smithsonian website
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