Florida ant species collects skulls, uses chemical weapons to kill prey

Nov. 16 (UPI) -- Florida is filled with strange creatures, but skull-collecting ants are near the top of the creepy list.

"In 1958, shortly after this ant was described as a species, scientists reported something weird about it," Adrian Smith, an entomologist at North Carolina State University, said in a news release.

Researchers found dozens of decapitated heads of trap-jaw ants in the nests of the newly discovered ant species, Formica archboldi. Scientists theorized the species either uses the abandoned nests of trap-jaw ants or is specially equipped to hunt their ant relatives.

Until now, however, scientists haven't studied the behavior of skull-collecting ants in detail.

"This was a study that grew out of reading a peculiar observation in a 60-year-old research paper," said Smith. "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."

The new research -- published this week in the journal Insectes Sociaux -- determined skull-collecting ants regularly prey trap-jaw ants.

The aggressors are able to sneak within striking distance thanks to a scent similar to that of their prey. When trap-jaw ants wander too close, Formica ants release a chemical spray composed of formic acid. Ants typically use an acid spray as a defense mechanism, but the skull-collecting ant has adopted the spray as a chemical weapon.

Smith and his colleagues observed the chemical attacks up close using high-speed video recording. Researchers watched the spray quickly immobilize the ants' prey.

Researchers were particularly intrigued by the species' chemical camouflage. Typically, ants use the layers of wax that coat their abdomen to communicate with their nest mates.

"It's really unusual for an ant species to display this much variation in chemical signature," Smith said. "Also, chemical mimicry is usually a tactic used by social parasites, but there's no evidence that F. archboldi are a parasitic species."

Though researchers can't yet confirm the chemical mimicry is purposeful, the new research suggests a long evolutionary history between skull-collecting and trap-jaw ants.

"Formica archboldi is the most chemically diverse ant species we know of. Before this work, it was just a species with a weird head-collecting habit. Now we have what might be a model species for understanding the evolution of chemical diversification and mimicry."