The study, conducted by researchers at the Museum, Columbia University, and Kyushu University, was recently published in the journal Nature Communications.
Advanced sociality, or eusociality, is a phenomenon common to insects like bees, ants, and termites—one known for the ways it breaks reproductive specialization into castes of workers and queens. Social insects are commonly targeted by parasitic beetles that are adapted to live inside colonies, where they consume not only nest resources, but sometimes even the nest's young.
The researchers used advanced imaging to study a beetle fossil, Mesosymbion compactus, that was trapped in Burmese amber 99 million years ago—right around the same time that ants and termites showed the first signs of eusocial behavior.
What they saw surprised them. This ancient fossil already featured specialized anatomy including a horseshoe crab-like body shape—which acts like a defensive shield—a modified head that faces backward, and thick, compact antennae. Millions of years later, these same features help modern beetle species invade colonies and withstand host attacks.
The presence of all of these traits in the fossil suggests that even early in the history of eusociality, M. compactus was likely a social parasite.
“Our new fossil is basically paleontological evidence that social parasitism is an unavoidable, negative counterpart of eusociality,” said Joseph Parker, one of the study’s authors and a research associate at the Museum and researcher at Columbia University.