Editor's Note 03/22/23: The authors of this study have issued a retraction after the provenance of a specimen was called into question by independent researchers. “While museum labels remain the most common manner in which specimen provenance is established, we should have exhibited more caution regarding specimen provenance and deeply regret this error,” the authors wrote.
While you might think that ants are widespread across the world, army ant species have been notably absent from Europe. These voracious predators are famous for cooperative foraging in massive groups capable of consuming over half a million prey items in a day. However, the discovery of ant species preserved in amber shows that the oldest army ant in the world lived across Europe around 35 million years ago.
“We didn’t think they were in Europe," Christine Sosiak, the paper’s lead author and New Jersey Institute of Technology Ph.D. candidate, told New Scientist. “It’s actually completely unheard of to find them there. And yet here we have this army ant, from so far back in history!"
The ant in question had been kept in the Museum of Comparative Zoology at Harvard University for nearly 100 years after being mislabeled as a common ant species. Preserved in Baltic amber, this specimen dates back to the Eocene and is only the second-ever army ant fossil to be described and the first to be recovered from the Eastern Hemisphere.
“I happened to come across a tiny specimen labelled as a common type of ant while gathering data for another project,” said Sosiak in a statement. “Once I put the ant under the microscope, I immediately realized the label was inaccurate … I thought, this is something really different.”
Only 3 millimeters (0.1 inches) long, the fossil is called Dissimulodorylus perseus, an eyeless species named after Perseus from the ancient Greek tales of the hero that defeated Medusa without looking directly at her. The fossil highlights the previously unknown ancestry of lineages of army ants that would have crawled around Europe before their extinction.
By conducting photography and CT scan analysis of the preserved specimen, the team think that D. perseus is a close relative of a species called Dorylus, which is found in Africa and Southern Asia. The team also discovered that D. perseus had an enlarged metapleural gland, suggesting that this species had a similar subterranean lifestyle and lived in large colonies.
"Because these army ants are blind, they use chemical communication to stay coordinated with one another to take down large prey,” explained Sosiak. “This worker may have strayed too far from its fellow hunters and into sticky tree resin, which eventually solidified and encased the ant as we see it today.”
The paper is published in Biology Letters.