Bombardier beetle

I should have been doing more fieldwork today, but heavy rain stopped play and I had a welcome day at home. Mind you, it was not really a relaxing day. Alex had to complete an assignment reviewing his work experience, which proved as hard as getting blood out of a stone.

Chris had returned from Gran Canaria in the small hours of the morning (which I slept through) and was putting the finishing touches to his Masters thesis, which was to be submitted tomorrow. At one point I really felt that fieldworking in the rain might have been preferable, especially when Word decided to crash, losing some of Alex's report.

I didn't get out to take any photographs, but just after 11pm I decided to photograph a couple of the rarer species that we'd found on our brownfield sites. This is the Bombardier Beetle Brachinus crepitans, a very local species predominantly found in southern Britain, which defends itself by emitting a powerful burst of boiling hot toxic gas, hence the name. Luckily this one wasn't too bothered by me.

The mechanism which enables it to do this involves precision engineering and may be used to improve the delivery of liquids in a number of fields, including inhalers and fore extinguishers. You can read about it below if you're interested.

The bombardier beetle is remarkable in that it can fire a powerful jet of hot, toxic fluid to fight off predators such as birds and frogs. While the chemical reaction that makes the venom has been understood for some time, the actual power behind the venomous squirt, which can travel as far as 20cm, has been cause for speculation.

Quantities of hydroquinone and hydrogen peroxide gases build up in the beetle's abdomen but, when necessary for defence, get mixed together in a connected 'combustion chamber' to produce toxic benzoquinone. This hot fluid is then fired off at force in the face of enemy predators.

The key to the beetle's powerful defensive trick is in its combustion chamber's inlet (or entry) and exit valves. The inlet valve opens to receive the chemicals, which begin to boil as soon as they meet, and closes when a sufficient amount of gas has been received.

As the gases react together, they generate heat and increase the pressure in the closed chamber. When the pressure reaches a critical point, the end of the exit valve is forced open and the hot fluid is ejected as a powerful burst of toxic steam in a process known as "flash evaporation".

Once the gas is released, the exit valve closes, the inlet valve opens and the chamber fills again, preparing for the next venomous ejection.