Secrets of Bombardier beetle's superheated defensive spray revealed

Shot of the bombardier beetle producing its distinctive defensive spray (Photo: Charles Hedgcock)

The bombardier beetle has a unique defensive mechanism. It induces a chemical explosion inside its shell to create a boiling, toxic liquid which it sprays at its aggressor. Now researchers in the US have discovered how it does this, and they hope that further study of the conditions inside the beetle that allow it to produce the jet without harming itself may inform real world technologies.

Previously, only external observations had been made of bombardier beetles as they produced the superheated spray. However, a team of researchers from MIT, the University of Arizona, and the Brookhaven National Laboratory were able to use high-speed synchrotron X-ray imaging to observe the intricacies of the process taking place inside the half inch beetle.

The boiling, superheated spray known as benzoquinone is created by combining two chemicals in a protective blast chamber located in the hindquarters of the beetle. The resultant chemical reaction boils the mixture, simultaneously creating the pressure required to expel it at a predator.

The pulsing nature of the spray appears to be generated passively, and may be the key as to how the bug survives the internal chemical explosions. The rate that the chemicals can be mixed is governed by the movement of a flexible membrane and a valve, which open and close an internal passage that connects a second chamber holding the precursor liquid to the blast chamber.

When the passageway allows the precursor liquid to flow through, the resultant explosion as it mixes with the chemical in the blast chamber stretches the membrane of the blast chamber, forcing the valve to close. Once the pressure is released via the expulsion of the newly created benzoquinone, the valve opens once more, allowing for the next explosion. By pulsing the spray, the bombardier beetle allows the blast chamber time to cool, preventing it from overheating and inflicting damage upon itself.

The bombardier beetle's sophisticated internal defense mechanism represents a stunning example of the complexity and beauty of natural evolution, but the team believes that continued observation of the process may reap real world technological benefits such as improved blast protection systems, and even the creation of new types of propulsion systems.

Check out the video below for footage of the bombardier beetle in action.

Source: MIT

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