Caught in the Act: Fossil Shows ‘Hell Ant’ Hunting With Headgear

A hell ant (right) locked in battle with the forerunner to the cockroach, frozen in time by amber. Fossils of predation are exceedingly rare. (New Jersey Institute of Technology / Chinese Academy of Sciences / University of Rennes, France)

(CN) — Scientists recently discovered a 99 million-year-old “hell ant” from the Cretaceous Period frozen in amber while locked in mortal combat with the ancestor of a cockroach. The ant was in the midst of dealing a death blow when both became trapped — sealing their fate. 

Hell ants, as they are colloquially known, are among the earliest ant species on record, and diverged from modern specimens prior to the most recent common ancestor of all ants. These insects’ novel features are unparalleled among the over 15,000 known ant species on the planet today. 

Discovered in Myanmar, the fossilized evidence of a species of hell ant, Ceratomyrmex ellenbergeri, that utilizes vertically articulating mandibles to attack its prey is a valuable find, according to a new study published Thursday in the journal Current Biology. Hell ants are believed to have disappeared around the Cretaceous-Paleogene extinction event 65 million years ago — the same event that wiped out the dinosaurs. 

Modern ants come equipped with lateral mandibles — their mouthparts close in and lock around prey from the sides. This study provides the first glimpse into how some extinct ant species differ from their descendants by engaging scythe-like mandibles to pin their quarry against a horn protruding from their forehead. 

Led by Phillip Barden, assistant professor in the Department of Biological Sciences at the New Jersey Institute of Technology, the authors sought to examine how these hell ants’ unique features came to evolve, how they were used and what evolutionary advantages they may have imparted. 

“Fossilized behavior is exceedingly rare, predation especially so. As paleontologists, we speculate about the function of ancient adaptations using available evidence, but to see an extinct predator caught in the act of capturing its prey is invaluable,” Barden said in a statement. “This fossilized predation confirms our hypothesis for how hell ant mouthparts worked… The only way for prey to be captured in such an arrangement is for the ant mouthparts to move up and downward in a direction unlike that of all living ants and nearly all insects.” 

Hell ants aren’t just a single species, they come in 16 unique varieties. A specimen discovered in 2017 by Barden and his team and aptly named Linguamyrmex vladi, after Vlad the Impaler, sports a metallic spike on its head, which presumably assisted in drinking the blood of its vanquished enemies. It’s fair to say that these were fearsome creatures at scale. 

Of the more than 50 ant species known to us from the Cretaceous period, only two are directly attributable to modern ants. Most belong to extinct lineages whose traits have long since ceased to be passed on — the most extreme example being haidomyrmecine, the infamous hell ant. Barden said they have long been suspected of capturing their prey by moving their mandibles vertically against their head, but until recently paleontologists lacked proof supporting that hypothesis. 

“This is an example of how phenotypic diversity is generated. I would say we have a mechanism for how really unusual features evolve,” said Barden in a telephone interview. “Before, we had all these strange species, and there was an open question to how and why they evolved to look that way. This paper confirmed the whole evolutionary pathway that generated that strange diversity.” 

While they may not appear so to the naked eye, ants are an incredibly diverse set of creatures adapted to survive in nearly every terrestrial environment. Their societies function much like a caste system, encompassing different roles for males and females, workers and queens. For example, worker ants are always female and evolved unique features suited to foraging, food processing, defense and brood care. 

These differing adaptations add to the species’ pool of genetic diversity over time and eventually lead to diverging evolutionary paths. As often turns out to be the case, however, not all adaptations are created equal. Species that have grown too well suited for a specific ecosystem typically find survival difficult once their environment changes. 

“We don’t know if their extinction is tied to their specialization, but we suspect that’s the case. Adaptations that fared the best in times of ecological change tend to be the most flexible,” said Barden. 

Barden added that a number of questions remain.  

“It’s looking more like ants had a pretty significant extinction event themselves,” he said. “The species we see after 65 million years ago are quite different. Why is it that some species go extinct and some don’t? Why are some adaptations and features static over millions of years?” 

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