
These ants decorate their homes with the heads of their enemies
We’re beginning to understand how and why one species goes after larger foes—and it may have something to do with evading kidnapper ants.
Scientists are beginning to solve a mystery involving three ants: A headhunter, a formidable biter, and a kidnapper.
For 60 years, scientists have known that one species of small, rust-colored ant known as Formica archboldi likes to decorate its nests with skulls, or head cases, of several kinds of trap-jaw ants.
This is bizarre, because trap-jaw ants come equipped with potent stingers and gigantic mandibles that can snap closed like a beartrap. These massive mouthparts come with some special features, such as allowing the insects to catapult to freedom when facing attack.
Diminutive F. archboldi ants, native to Florida and surrounding states, nevertheless succeed in taking them down and nabbing their heads—but how?
“Something weird was going on but no one had looked into it yet,” until now, says Adrian Smith, a research biologist at North Carolina State University.
In a new study published in the journal Insectes Sociaux, Smith has shown that F. archboldi subdues its quarry with quick, highly efficient sprays of toxic acid.

This is curious, says Smith, because while most of the ants in this family possess acid-spraying nozzles, they usually only deploy them as a means of last defense. F. archboldi, on the other hand, goes on the attack.
“They just seem to be sort of ready for the fight,” says Smith.
No one is sure why the headhunters should be such effective predators of trap-jaw ants, but it may have something to do with a waxy layer of scents ants produce called cuticular hydrocarbons. When Smith sampled these scents from F. archboldi, he found that they matched the species of trap-jaw ants they co-occur with almost perfectly.
It’s as if the lion were evolving to smell like the zebra or the rattlesnake the field mouse.



































Common sense would tell us that mimicking the scent profile of its prey gives the headhunter ants some advantage over them in battle. But Smith hasn’t seen any evidence of this.
But he does have another hypothesis, one that involves yet another ant species known to kidnap and brainwash entire colonies of F. archboldi.
It’s difficult to overstate how important chemical cues are to ants. While the animals have eyes, they rely on scents to allow them to follow their nestmates to rich food supplies, identify friend from foe, and even to avoid being mistaken as trash and ejected from the colony.
Headhunters, trap-jaws, and kidnappers
But some ants also use their scents as a cloaking device.
“So there’s this genus of ants called Polyergus. Their old common name was slave-making ants, but we use the term ‘dulotic ants’, or pirate or kidnapper ants,” says Smith.
Whatever you want to call them, they mean business.
Once a kidnapper ant queen identifies a headhunter ant colony, it sneaks in, murders the incumbent queen, and then “bathes in her bodily fluids,” says Smith. The imposter then uses this newly acquired scent profile to avoid detection while she pumps out a bunch of eggs. These hatch into a generation of workers whose only job is to go out and capture more Formica ants.
Now, because each kidnapper ant species typically parasitizes just one species of Formica ant, Smith says there’s a pretty good evolutionary incentive for the Formica ants to keep changing their scent profiles in an attempt to throw the kidnappers off their game.
In fact, it’s possible that this is why the headhunter ants have evolved to smell like trap-jaw ants, the latter of which are not parasitized by the kidnappers. Not to gain advantage over the trap-jaws, mind you, but to disguise themselves as another species.
“But I have no evidence for that at all,” says Smith. “It’s just pure speculation.”
A co-evolutionary relationship
One thing is clear, at least. The matching hydrocarbon profiles are unlikely to be a coincidence, because the headhunter ants are only found in areas where there are also trap-jaws. What’s more, the headhunters have only been found to mimic native trap-jaw species, not ones that have been recently introduced.
All of which points toward a complex, co-evolutionary relationship between the headhunters and the trap-jaws, says Smith. Even if we don’t fully understand what that relationship is yet.
Other experts in these species found the new paper both surprising and befuddling.
“I find that Formica archboldi can take down, and even specialize, on large trap-jaw ants remarkable,” says Andy Suarez, an entomologist at the University of Illinois at Urbana-Champaign. “Subduing trap-jaw ants with their formic acid spray seems like something out of a Peter Jackson film.”
Corrie Moreau, an entomologist at the Field Museum of Natural History and a National Geographic Explorer, agreed that the new study was interesting. (Read: Meet the woman making ants the next big thing in biology.)
“Despite the careful analytical work done on this odd animal the question still remains, why do these ants surround their nests in the skeletons of their prey?” says Moreau. “I wonder if they use the dead bodies of their prey to mask themselves in the scent of their local prey species.”
“This just shows that the more you know about nature, the more questions you uncover," she says.
Related Topics
Go Further
Animals
- These 'trash fish' are among Earth's most primitive animalsThese 'trash fish' are among Earth's most primitive animals
- These photos are works of art—and the artists are bugsThese photos are works of art—and the artists are bugs
- The epic migration of a 6-foot long, 200-pound catfishThe epic migration of a 6-foot long, 200-pound catfish
- Frans de Waal, biologist who studied animal emotion, dies at 75Frans de Waal, biologist who studied animal emotion, dies at 75
Environment
- Are synthetic diamonds really better for the planet? The answer isn't clear-cut.Are synthetic diamonds really better for the planet? The answer isn't clear-cut.
- This year's cherry blossom peak bloom was a warning signThis year's cherry blossom peak bloom was a warning sign
- The U.S. just announced an asbestos ban. What took so long?The U.S. just announced an asbestos ban. What took so long?
- The most dangerous job? Inside the world of underwater weldersThe most dangerous job? Inside the world of underwater welders
- The harrowing flight that wild whooping cranes make to surviveThe harrowing flight that wild whooping cranes make to survive
History & Culture
- Who is Hanuman, the Hindu god with the face of a monkey?Who is Hanuman, the Hindu god with the face of a monkey?
- Why Swedish children celebrate Easter by dressing up as witchesWhy Swedish children celebrate Easter by dressing up as witches
- Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’
- A surprising must-wear for European monarchs? Weasels.A surprising must-wear for European monarchs? Weasels.
Science
- LED light treatments for skin are trendy—but do they actually work?LED light treatments for skin are trendy—but do they actually work?
- NASA smashed an asteroid. The debris could hit Mars.NASA smashed an asteroid. The debris could hit Mars.
- Humans really can have superpowers—scientists are studying themHumans really can have superpowers—scientists are studying them
- Why engineers are concerned about aging infrastructureWhy engineers are concerned about aging infrastructure
Travel
- Welcome to Hydra, the Greek island that said no thanks to carsWelcome to Hydra, the Greek island that said no thanks to cars
- How to plan a food weekend on the Greek island of TinosHow to plan a food weekend on the Greek island of Tinos
- Are these the most charming villages in Catalonia?
- Paid Content
Are these the most charming villages in Catalonia?







