In the quiet woodlands and grasslands of Florida, a war is being fought beneath our feet—a war of survival, strategy, and chemical deception. The unlikely soldiers in this conflict are ants, specifically the Skull-Collecting Field Ant (Formica archboldi), and their deadly prey, the Trapjaw Ant (Odontomachus sp.) But there’s more to this story than predator and prey. Lurking in the background is an even more sinister enemy—the Floridian Slave Raider Ant, (Polyergus oligergus.)
For decades, scientists have puzzled over Formica archboldi’s strange behavior. While other Formica ants are generalists, feeding on a variety of insects and scavenging for food, Formica archboldi has developed a peculiar taste for trapjaw ants. More than that, their nests are strewn with the decapitated heads of their trapjaw victims—a macabre collection that earned them the nickname "skull collectors." But why?
Skull Collecting Ants and the skulls of trapjaw ants
The answer may lie in the chemical arms race that shapes life in the ant world.
Trapjaw ants are formidable opponents. Their spring-loaded mandibles snap shut at lightning speed—over 230 kilometers per hour—and they can deliver painful stings. Yet, somehow, the skull collectors have become an adept predator of these fierce ants.
The Trapjaw Ant Executioner
In a series of tests, study author Adrian Smith from the North Carolina Museum of Natural Sciences placed live trap-jaw ants in an arena with either Formica archboldi or F. pallidefulva — a similar species, but which doesn't specialize on hunting trapjaw ants.. The ants were put into a small "28 mm fight arena," where their aggressive encounters were filmed in slow motion.
Formica pallidefulva (Pale Field Ant) and Formica archboldi (Skull Collector Ant) in fights with the Odontomachus (Trapjaw Ant)
The results showed that in 1 out of 10 trials, F. pallidefulva managed to incapacitate the trap-jaw ant, leaving it unable to move around the arena, although it wasn’t completely paralyzed. But the skull collecters were able to incapacitate the trap-jaw ant. In 7 of those interactions, it was fully immobilized.
Both Formica species rely on formic acid spray to defend themselves and neutralize opponents. The chemical makeup of the spray is the same for both species, so F. archboldi’s success doesn’t seem to come from a more powerful spray.
Smith speculates that the skullcollectors may simply be more precise or effective at deploying the spray, though further study is needed to confirm this.
The Chemical Disguise
After defeating them, the field ants bring the trapjaw bodies back to their nests, decapitating them and scattering their skulls around the entrance. This grisly display isn’t just for show. Researchers theorize it may serves a far more strategic purpose.
Ants communicate largely through chemicals, particularly the hydrocarbons on their cuticles, which act like ID badges. By recognizing these chemical signatures, ants can distinguish nestmates from enemies. In a surprising twist, the skull collectors don’t just kill trapjaw ants—they chemically mimic them. Their cuticular hydrocarbon profiles closely match those of the trapjaw species they prey on, such as the Brown Trapjaw Ant, Odontomachus brunneus and Relict Trapjaw Ant, O. relictus. Over time, as Formica archboldi continues to collect trapjaw skulls and blend in with their scent, their nests begin to smell less like a field ant colony and more like a trapjaw stronghold.
Hiding from the Slave Raider Ant
It's theorized that chemical disguise might protect the field ants from Polyergus oligergus, the slave-raiding ant that terrorizes them. The slave raiders are specialized parasites that invade Formic colonies, kidnapping their young and raising them as workers in their own nests. Scouts from the Slave Raiding Ant colony search for vulnerable Field Ant nests, but attacking a nest filled with aggressive, fast-jawed trapjaw ants could be a dangerous mistake. By surrounding themselves with trapjaw skulls and masking their own scent, Formica archboldi might be tricking the raiders into thinking twice before launching an attack.
If true, this would be a rare and remarkable case of a non-parasitic species adopting a parasite-like chemical mimicry to outsmart their own parasites.
Testing this theory would require looking closer at how Polyergus oligergus identifies its hosts and how it reacts to the chemical signatures of trapjaw ants. If the raiders are fooled by this mimicry, it could reveal a whole new layer of complexity in the battle between these ants—a war not only of physical strength but of chemical deception.
In this hidden world, the stakes are high, and survival depends on more than brute force. By mastering the art of chemical camouflage, Formica archboldi has turned the bodies of its enemies into shields, protecting their colony from a fate worse than death: enslavement.
So, next time you find yourself walking through the fields of Florida, remember that beneath your feet, a fierce battle is taking place—one where the victor isn’t always the strongest, but the most cunning.
Further Reading
de la Mora, A., Sankovitz, M., & Purcell, J. (2020, January 1). Ants (Hymenoptera: Formicidae) as host and intruder: recent advances and future directions in the study of exploitative strategies. Myrmecological News. https://doi.org/10.25849/myrmecol.news_030:053
Smith, A.A. Prey specialization and chemical mimicry between Formica archboldi and Odontomachus ants. Insect. Soc. 66, 211–222 (2019). https://doi.org/10.1007/s00040-018-0675-y
Trager, J. C. (2013). Global revision of the Dulotic ant genus Polyergus (hymenoptera: Formicidae, Formicinae, formicini). Zootaxa. https://mapress.com/zt/article/view/zootaxa.3722.4.5
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