0509ctt bombardier lo res


An episode of National Geographic Wild shows a ground beetle (the group of which includes bombardier beetles) spraying its noxious chemicals. Credit: NatGeoWild; Youtube

Love ‘em or hate ‘em, insects are everywhere. They are the most diverse, most numerous, and most widespread of any animal on the planet. And some of these species have evolved some uniquely interesting defenses to evade attackers.

Bombardier beetles have one of the most elaborate arthropod defenses—the tricky little bugs can actually spray noxious chemicals out their rear end to very effectively kill or keep attackers at bay.

The bombardier beetle’s defense is simple chemistry—it stores reactive hydroquinones and hydrogen peroxide in separate compartments in its abdomen. When threatened, the beetle can squeeze its muscles to combine the chemicals into a mixing chamber. Enzymes in the chamber catalyze an exothermic reaction that heats up the bug’s butt, vaporizing part of the mixture and creating a pressure buildup that allows the bug to jet the mixture right into the face of an unlucky attacker. Watch the video above to see the beetle’s butt in action. 

Researchers at ETH Zürich have taken the bombardier beetle’s example to develop a similar defense system that could eventually protect ATM machines from would-be thieves.

“When you see how elegantly nature solves problems, you realize how deadlocked the world of technology often is,” says ETH chemistry and applied biosciences professor Wendelin Jan Stark.

Instead of separate chemical chambers, however, the researchers engineered plastic films with honeycomb structures to enclose chemicals. The two chemicals the team mixed were hydrogen peroxide and manganese dioxide, which economically replaces the need for enzyme catalysts. Stacking two films containing the separate reactive chemicals on top of each other, separated by a clear lacquer layer, allows the device to remain poised for action. If a disturbance breaks the lacquer layer, the chemical mixture “triggers a violent reaction that produces water vapor, oxygen and heat,” according to an ETH press release.

The researchers report in the release that “the product of the reaction in the film is more of a foam than a spray when compared to the beetle.” The evolution of this foam can be seen in the images below, where infrared shows that the reaction generates foam that heats up to 80°C. 


Foam is released by the self-defending film. Credit: ETH Zürich

Although the new materials are modeled after the bombardier beetle, unlike the bug, the idea is not to spray the chemicals at a would-be-thief. Instead, the foam would be used to make tender useless by soaking it with foam containing dye and DNA-enveloped nanoparticles (for tracking purposes) when the machine is tampered with.

Some ATMs already come equipped with security systems that spray thieves or tender upon attack, although these existent systems rely upon mechanical setups that are both expensive and prone to error. The new bombardier beetle-styled chemistry could be implemented on ATMs for only about $40, according to the press release.

The simple and affordable system could help prevent thieves from tampering with machines or driving off with the whole machine in tow.

The paper, published is Journal of Materials Chemistry A, is “Self-defending anti-vandalism surfaces based on mechanically triggered mixing of reactants in polymer foils” (DOI: 10.1039/C3TA15326F).

Feature image credit: jayvee18; Fotolia; ETH Zürich