Beetles are a wonderful example of this variety. They all have a broadly similar body plan with chewing mouthparts and a hardened pair of wing-cases, but you only have to look at the selection of beetles on display in Bug Lab to get a taste for how that basic form is shaped for a variety of different purposes. For example, we have the male harlequin beetle with bizarrely long front legs used in pushing contests to compete for mates and territory. There’s a diving beetles streamlined body with legs adapted for easy movement through water. There are stag beetles with huge heads and jaws for jousting and at the other end of the scale there’s a beetle with a narrow head to make it easier to get into the shells of snails it hunts. There’s more to see than that, including our Exoskeleton hero in giant form, the bombardier beetle.
Our bombardier beetle is represented in rather whimsical fashion as a slide (and yes, adults are welcome to try it too). You blast out the bottom end, which is appropriate as that is the bombardier beetle’s claim to fame. Bombardier beetles are like living machine guns, sending out a near boiling chemical spray at a rate of hundreds of pulses a second out of a nozzle located on the rear end. It’s a sure-fire way to get your enemies to leave you alone. It’s all fuelled by chemical explosions inside the beetle’s body. Hydroquinones and hydrogen peroxide are broken down by enzymes in a chamber. This reaction makes water, oxygen and a substance called para-quinone which is incredibly irritating and unpleasant. The reaction is explosive, releasing a lot of heat, vaporising a portion of the mixture and generating pressure as well. This pressure is enough to eject the spray and causes a flexible part of the chamber wall to close off like valve, saving the beetle from being blown up by its own weapon system. In Bug Lab there’s film of the inner workings of a blasting bombardier beetle made as part of Eric Arndt’s doctoral research. Eric needed a half-billion dollar machine called a synchrotron (a high-speed x-ray) to get the footage! It’s thought that all the chemicals and systems involved are derived from the exoskeleton and the chemicals needed to harden them, as well as common beetle defensive chemicals.
