These Tiny Ants Crawled All Over Larger Ants and Licked Them Clean. Scientists Aren’t Sure How This Behavior Benefits Any of Them

After witnessing the interactions in an Arizona desert, a Smithsonian researcher suggests that the little ants picked off tasty treats and that the big ants got thoroughly groomed in hard-to-reach places

Margherita Bassi | Daily Correspondent

April 16, 2026

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Twenty years ago, entomologist Mark Moffett was in southeastern Arizona when he noticed insects doing something strange. Red harvester ants parked themselves near the nests of much tinier cone ants, and then got a spa treatment from the teensy critters.

This previously undescribed dynamic, which Moffet details in a study published April 12 in the journal Ecology and Evolution, represents the first known observation of a possible “cleaner” ant, one that grooms another species. The benefits of this behavior, however, remain mysterious.

During that 2006 trip, Moffett, of the Smithsonian’s National Museum of Natural History, witnessed quarter-inch-long harvester ants in the mesquite desert that “seemed frozen in place,” he writes in the study. Each stood still like a statue—an odd behavior for the busy female workers—and cone ants roughly one-third their size climbed onto them.

Ants tend to be aggressive towards other species, so he initially assumed that’s what was going on, Moffett says in a 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.”

Over the next five days, he observed at least 90 of these interactions, snapping photos along the way.

The activity started at sunrise and peaked before 9:00 a.m., after which the ants hid from the heat of the day. A harvester ant would approach a cone ant nest and stand stiffly, high on her legs, and hold her mandibles open. Then, a cone ant would emerge, typically within a minute, crawl onto the client, and get to work licking, nipping and pulling.

Up to five cone ants would join each cleaning effort, and spa treatments lasted from a few seconds to more than five minutes.

Moffett put the photos away, thinking he would need to gather more data to understand the ants’ interactions, he tells the New York Times’ Alexa Robles-Gil. But after taking another look at them more recently, he realized he “had the whole story in pictures.”

The cone ants were determined to be an undescribed species belonging to the Dorymyrmex genus. According to Moffett, they are equivalent to cleaner fish, which—as the name suggests—wash parasites, mucus and dead skin off other animals. These cleaner ants seemed to do a thorough job, even tidying up between the harvester ants’ open jaws. Interestingly, the cone ants did not try to clean dead harvester ants that Moffett put outside their nests.

“What surprised me was the intimate interaction between this huge ant with these gigantic mandibles, and then this tiny, little ant delicately moving among the mouth parts, basically looking fearless in there,” Alexandra Grutter, a marine ecologist at the University of Queensland in Australia, who Moffett consulted about the ants’ behavior, tells the Times.

The big harvester ants endured their cleanings without biting. However, when a worker decided her spa visit was over, she flung the cone ants off so vigorously that she often flipped onto her back.

Still, Moffett doesn’t know exactly how each party benefits from the relationship. He proposes that the cone ants get to eat tiny calorie-rich crumbs on the larger species, possibly flakes from the seeds eaten by the harvester ants. The clients might be getting a more thorough cleaning than achieved through their within-species grooming. Perhaps the teensy cone ants can access those hard-to-reach areas, Moffett posits.

“It certainly looks like a mutualism,” Joe Parker, an evolutionary biologist at Caltech who Moffett also consulted, tells Science’s Erik Stokstad. “The payoff must be pretty substantial for this interaction to evolve.”

Additional research is needed to understand what each species gains through this behavior. Specifically, researchers should examine whether the grooming diminishes harvester ant infections, or if the activity ameliorates either species’ microbiome, Moffet suggests.

“All kinds of amazing discoveries are still there to be made outside of the lab,” he says in a statement. “Finding new species and behaviors in nature often requires us to pay close attention to the small things—including the ants.”

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.