Small Ants Observed Cleaning Large Ants in the Arizona Desert — a New Behavior in Insects
Insect expert Mark Moffett visited Portal, Arizona, in June 2006, ready to study bugs at the nearby Southwestern Research Station. Little did he know that he would make a discovery on his first morning — not at the Station, but around the back of the cottage he was staying in.
Moffett recorded an unusual interaction between two ant species that he had never seen reported before. Small cone ants climbed all over larger harvester ants, appearing to clean their body. Two decades later, Moffett has now published his observations in the journal Ecology and Evolution, partly because no other reports of these “cleaner” ants had been recorded in that time.
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Two Ant Species Working Together
On the morning of his discovery, Moffett was drinking a cup of coffee while watching harvester ants (Pogonomyrmex barbatus) as they left their nests. Most of the insects were roaming around, but a couple, he noticed, were frozen in place with their jaws open and legs extended out. He realized that these ants were covered in, well, ants.
“Given the usual tendencies of ants, I first assumed that I was observing aggression,” said Moffett in a press statement. “But the larger ants seemed to seek the attention of the smaller ants by first visiting their nests and then allowing the small ants to lick and nibble all over them.”
These smaller ants, which he has since concluded are from an unidentified species of cone ant (Dorymyrmex), were exploring the larger ants’ bodies, nipping and licking at their carapaces. The harvester ants, if they wanted, could have devoured the smaller ants easily — some were even cleaning inside the larger insects’ jaws — but instead they stood entirely still, waiting for the cone ants to get their fill.
“This new ant species is the insect equivalent of cleaner fish in the ocean,” said Moffett. Cleaner fish roam the ocean, looking for larger fish that are pestered by parasites or covered in dead skin. They then clean the larger fish’s scales. The larger fish, like the harvester ants, are happy to let the cleaning happen, even when the bigger fish would usually predate the cleaners.
Observing Ant Interactions
Moffett took high-resolution photographs of the cleaning behavior and recorded more than 90 interactions between the two ant species over the next few days. All interactions involved the same behavior: harvesters would wander up to cone ant nests, get into position, and await their cleaner. Sometimes up to five smaller ants would arrive to clean a harvester at once.
Some cleans lasted only seconds, while Moffett saw others lasting more than five minutes. Eventually, the harvesters would shake off the smaller ants with enough force that they sometimes flipped the smaller ants upside down. Cleaning time was over.
Moffett said he has not been able to find any other record of this behavior in other insects. While the interactions between cleaner fish and their parasite-ridden clients are well-understood — one fish gets food, the other gets rid of bugs or pesky dead skin — it’s less clear what the two species of ants gained from their interaction.
Moffett suspects their motivations may be similar, but future research exploring the potential health benefits either species gains from grooming will answer the question in more detail.
“All kinds of amazing discoveries are still there to be made outside of the lab,” Moffett said. “Finding new species and behaviors in nature often requires us to pay close attention to the small things — including the ants.”
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