Like fierce humans who lived before them, a certain type of ant in Florida keeps a home that’s surrounded by the skulls of its enemies. In the ‘50s, soon after this ant species was discovered, scientists noticed that Formica archboldi nests were littered with torn parts of other ants. Decades later, scientists have uncovered the reason why.

In a study released this month in Insectes Sociaux, research biologist Adrian Smith, Ph.D. reveals that ant heads don’t end up in Formica nests by chance. Instead, they are the remains of victims that turn into dinner. The victims are a species called Odontomachus, or trap-jaw ants, which are themselves dangerous, carnivorous insect predators with mandibles capable of opening 180 degrees.

While previous theories held that Formica ants innocently inherited trap-jaw ant nests, Smith’s research demonstrates that Formica ants chemically mimic their prey and spray them with formic acid (also found in a beel’s stinger), then drag the bodies to their home. The video above shows these battles as they play out. The chemical attack Formica uses isn’t any different than that of the trap-jaw ants, but luckily for the former, they are more effective sprayers.

Smith, head of the Evolutionary Biology and Behavior Lab at the North Carolina Museum of Natural Sciences and an assistant research professor at North Carolina State University, tells Inverse that this type of chemical mimicry is typically only found in parasitic ant species, which usually enter into the nest of another species and then exploit their victims.

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A *Formica archbolid* ant surrounded by trap-jaw ant skulls.

“There is no evidence that F. archboldi is parasitic, so that makes it unusual,” Smith explains. “Additionally, because F. archboldi chemically mimics 2 species of trap-jaw ants across Florida, it is the most chemically diverse [in hydrocarbons] ant that we know of.”

It’s theorized that these ants evolved to demonstrate this chemical mimicry as a defense mechanism. By disguising themselves as trap-jaws, they likely avoid certain levels of aggression from trap-jaws and other ants. In turn, they become the aggressor. Lab experiments showed that, after a chemical attack, Formica ants treat trap-jaws like food. They grab, pull, and lick their victims until they degrade into pieces and, in the process, their heads pop off.

“In field colonies, it’s common to find even the head cases hollowed out with the mandibles removed,” Smith says. “So, it’s not impossible that the contents of the head itself are used as food for members of the colony.”

One of Smith’s favorite things about this study is that “this story has a lot left to discover.” He started the study for no other reason that to explore a weird natural history discovery made 60 years ago. Now, research and lab experiments have made way in explaining an entomological oddity.

“The study was based on the notion that these little ants were probably doing something weird and no one had looked into it,” Smith says. “It was purely exploratory and descriptive, and now, from studying this tiny bit of ant trivia, we have what might be a model system for studying chemical diversity and mimicry.”

Photos via Adrian Smith (1, 2)