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Mystery of ‘headhunting’ ants solved © Adrian Smith

Mystery of ‘headhunting’ ants solved

Published: 28th January, 2019 at 00:00
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The Formica archboldi ant decorates its nests with the severed heads of the bigger, nastier prey it kills - now we know how.

In the late 1950s, researchers in Florida made a macabre and perplexing discovery: ants known as Formica archboldi were decking out their nests with the severed heads of much larger and more aggressive trap-jaw ants. Ever since the discovery, the bizarre behaviour has puzzled entomologists – just how are the ants capable of it?

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Now, by observing the ants with high-speed cameras placed in their nests, researchers at North Carolina State University think that they have the answer.

F. archboldi are able to ‘disguise’ themselves as trap-jaw ants, as the cocktail of waxy substances that coats their bodies is chemically similar to that of two species of trap-jaw ant. This means they can then approach their prey unnoticed before paralysing them by spraying them with a concentrated burst of formic acid – a behaviour usually only seen when the ants are defending themselves. F. archboldi then finish the job with their powerful jaws before dragging the corpses of the trap-jaw ants into their nests and systematically dismembering them.

“This was a study that grew out of reading a peculiar observation in a 60-year-old research paper. Odds were that these ant heads weren’t in Formica nests by chance and that there was some interesting biology behind this natural history note,” said Prof Adrian Smith, the head of North Carolina State University’s evolutionary biology and behaviour research lab.

“The scientifically surprising finding of this study was that these ants chemically match or mimic the chemical profiles of two species of trap-jaw ant. It’s really unusual for an ant species to display this much variation in chemical signature. Also, chemical mimicry is usually a tactic used by social parasites, but there’s no evidence that F. archboldi are a parasitic species,” Smith added.

How strong are ants? © Getty Images

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Authors

Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.

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