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Nature

These Skull-Collecting Ants Are Way More Metal Than You

author

Dr. Katie Spalding

Freelance Writer

clockNov 19 2018, 16:44 UTC

I am the punishment of God. Photo credit: Adrian Smith

When ancient cultures wanted to strike terror into their enemies, they knew exactly how to do it. Tales of Celtic tribes decapitating their foes and displaying the heads on spikes and nails spread through the Roman Empire like wildfire. It sent a clear message – “don’t mess with us.”

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We may never know how exactly these ancient Europeans got their predilection for head-hunting. But had they lived in Florida, they might have got their inspiration from the local insect population.

Formica archboldi looks like a fairly boring ant. They’re not particularly big, or brightly colored, and they’ve been more or less ignored since they were originally described in 1958. But in a state where giant alligators roam golf courses and invade backyards, zombie warnings are a real thing, and the randomized mania of Florida Man is ever-present, Formica archboldi somehow manages to be the most badass creature around.

See, there’s something strange about F. archboldi. Their nests are littered with the decapitated heads of trap-jaw ants – a fearsome predator with a powerful sting and one of the fastest bites ever recorded.

“Add 'skull-collecting ant' to the list of strange creatures in Florida,” said Adrian Smith, head of the Evolutionary Biology & Behavior Lab at the North Carolina Museum of Natural Sciences. And his research, published this week in the journal Insectes Sociaux, explains just how these miniature barbarians are able to take on the trap-jaws so successfully.

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In a set of gladiator-style battles, Smith put F. archboldi face-to-face with various trap-jaw species and filmed the ensuing fight. To see what was so unique about F. archboldi’s tactics, this trial by combat was also faced by F. pallidefulva – a fellow Formica species, but one without a history of somehow butchering predators much deadlier than itself.

Like most ants, F. archboldi can spray formic acid at its enemies as a defense mechanism – a sprayed trap-jaw will be immediately disabled, unable to walk or stand. But compared to its Formica brethren, archboldi’s acid isn’t particularly strong – so the ant instead relies on much more refined tactics to take down its foe.

It turns out, F. archboldi are just more efficient sprayers than other kinds of ant, immobilizing the trap-jaws a full 10 out of 10 times compared to F. pallidefulva’s one lone success. And even more deviously, it seems F. archboldi may be chemically mimicking their enemies, transforming their defense spray into a targeted weapon.

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"The scientifically surprising finding of this study was that these ants chemically match… the chemical profiles of two species of trap-jaw ant," explained Smith. “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.”

The obvious question, of course, is why these otherwise-nondescript ants are so good at killing trap-jaws – and why they choose such a gruesome décor for their nests. And while Smith stresses that more research is needed to answer this, he does have a hypothesis or two.

“I think they’re somehow feeding off of [trap-jaws], because the trap-jaw ant body parts are hollowed out in the nest,” he told The Verge. “You find some abdomens that are cracked open and totally empty.”

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After six decades of languishing in ant-nonymity, this study now makes F. archboldi the most chemically diverse ant species known to science.

“Before this work, it was just a species with a weird head-collecting habit,” explained Smith. “Now we have what might be a model species for understanding the evolution of chemical diversification and mimicry.”


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