The innocuous looking bombardier beetle is one of the most remarkable creatures around. This tiny insect is endowed with a defence mechanism that would be the envy of any comic-strip superhero — it can fight off any spider, frog, ant or bird that comes too close by blasting the attacker with a powerful jet of hot, toxic fluid. Furthermore, the beetle can aim its weapon in any direction (even over its head) with pinpoint accuracy, and can reach distances of up to 20 cm with its spray.
The bombardier beetle, which is rare in Europe but common in Africa, Asia and warmer parts of the US, forms its noxious spray by reacting small amounts of hydroquinone with hydrogen peroxide in the presence of the catalysts catalase and peroxidase in a pair of combustion chambers in its abdomen. This exothermic reaction produces a toxic solution of benzoquinone, other chemicals and water, and heats the solution (which is mainly water) to above its boiling point. Although some details of the chemical process have been known for years, until recently scientists did not understand how the beetle managed to eject this solution so powerfully.
In the April issue of Physics World, Andy McIntosh and Novid Behesghti reveal how this puzzle has now been solved, which has inspired many developments in the field of spray technology.
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