Parasitic Beetle Revealed in Amber Fossil

Research posts

A newly discovered 99-million-year-old fossil suggests that as soon as ancient insects began forming colonies, their nests became targets for parasitic beetles. The study, conducted by researchers at the Museum, Columbia University, and Kyushu University, was recently published in the journal Nature Communications.

 

Mesoymbion rove beetle fossil suspended in amber (left); laser scanning shows x-ray views of the beetle (right).

Mesosymbion rove beetle fossil in amber (left), with laser scanning confocal images of the back and underside of the beetle (middle and right).

© J. Parker


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.

 

Detailed view of Schedolimulus (left) and Termitodiscus (right) as they cling to the honeycombed walls of termite nests.

Modern rove beetle social parasites photographed on the walls of termite nests. (left) Schedolimulus; (right) Termitodiscus.

© T. Komatsu


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.

 

Drawing of a beetle with two thick antenna and armored-looking head and body (left); x-ray view of Mesoymbian's head (right).

Model reconstruction of Mesosymbion (left); confocal laser scan of the head of Mesosymbion (right).

© J. Parker (left); © J. Parker (right)


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.

 

Three modern rove beetles display their horseshoe-crab-shaped heads and scaled bodies.

Modern rove beetle social parasites, with the same horseshoe crab-like, defensive morphology as Mesosymbion.

© T. Kanao


“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.

 

Intrigued by fossil beetles? Read about Joseph Parker's prior research on the subject.