Secrets of the semi-automatic, pump-action beetle

SCIENTISTS HAVE captured the marksmanship of the bombardier beetle on film for the first time, showing it to be the gunslinger of the insect world.

With the accuracy of a sniper's bullet, the bombardier beetle can shoot from the hip - or abdomen - with a deadly cocktail of boiling hot acids.

Two pump-action abdominal glands can smother a potential enemy with acidic artillery in a fraction of a second, buying time for the beetle to escape by unfurling its cumbersome wings and flying away.

Bombardier beetles, which live on the ground in tropical countries and are under constant threat from predators such as ants, have developed a unique defensiveweapon based on two separate glands full of chemicals.

When the contents of the larger gland - containing hydrogen peroxide among other substances - are mixed with the enzymes of the second, an explosive reaction takes place, liberating oxygen, which is used as a propellent to fire the acidic substances several inches from the insect with an explosive popping sound.

The heat generated by the chemical reaction can cause the temperature of the spray to reach 100C, making it evenmore uncomfortable for any creature that dares to get in the beetle's way.

Entomologists have long been impressed by the bombardier beetle's marksmanship but until now have not been able to confirm how accurately it can swivel its abdominal "hips" to fire up to 20 rounds without reloading.

Thomas Eisner and Daniel Aneshansley, scientists from Cornel University in Ithaca, New York, have taken high-speed photographs of the bombardier beetle in action and shown that it can aim the stream of hot liquid using a pair of shield-like deflectors operating in tandem at the tip of the beetle's abdomen.

The beetle is immune to its own lethal liquid so can also defend itself by accurately spraying parts of its body when being attacked by a swarm of smaller insects, such as ants.

"It can target its individual legs, and even the individual segments of its legs. Moreover, in aiming at a leg, it takes into account the postural orientation of that leg. The beetle is able even to target sites on its back," the researchers say in the journal Proceedings of the National Academy of Sciences.

"Although it was known that bombardier beetles can aim their spray by revolving the abdominal tip, the degree of precision with which they target their ejections had escaped notice," they say.