Ivette Perfecto/University of Michigan News Service

Uncovering the secrets of a beetle’s explosive, chemical spray

An unsuspecting ant crawls onto a still bombardier beetle, curious and perhaps looking for a meal. Then, without warning, the beetle’s rear end fires out a blast of boiling hot, toxic spray at the interloper, and then another and another before the ant flees. Scientists have long known that explosions in the beetle’s pygidial glands—a pair of abdominal structures that produce defensive secretions—power its spray, but until recently the creature’s tough exoskeleton had shrouded the blasts in mystery. Now, scientists have examined the volatile process in living beetles with the help of synchrotron x-ray imaging. When threatened, the beetle contracts muscles that open a structure called the interchamber valve, allowing a droplet of a mixture of hydrogen peroxide and chemicals known as hydroquinones to flow from one chamber in the gland to another, the team reports online today in Science. There, the droplet comes into contact with the peroxidase and catalysts that create the noxious chemicals and the reactions that explode them out of the insect’s rear. Pressure from the explosion distends a flexible structure called the expansion membrane, closing the interchamber valve and disrupting the flow of chemicals. When pressure in the chamber drops after the explosion, however, the valve opens again, and a new droplet begins the process once more. Such new insight could help improve technologies like fuel injectors in internal combustion engines, the researchers say.