The beetle with a built-in spray gun
Bombardier beetle (Brachinus crepitans)
Where you might see it
A small ground beetle found on chalky grassland in southern England, often hiding under stones by day. You are unlikely to catch it in the act, but when something threatens it, it fires a hot, stinging spray from its tail end with a sharp popping sound.
Nature's problem
A small beetle is an easy meal for frogs, birds and spiders, and it cannot outrun most of them. It needs a way to startle and sting an attacker far bigger than itself, and buy enough time to escape.
Nature's solution
The beetle keeps two harmless liquids in separate stores inside its body. When it is attacked, it squirts them together into a tiny chamber where they react, heat up to almost boiling, and burst out as a fast spray — fired in rapid pulses, like a string of tiny pops, and aimed with surprising accuracy at whatever is bothering it.
What people made
Engineers studied how the beetle fires its spray in quick pulses and copied the idea to design better sprays and engines. Copying the beetle's pulsing chamber helped make finer mist from medicine inhalers and fire extinguishers, and cleaner bursts of fuel inside car engines — sprays that travel further and waste less. This one was studied and copied on purpose, the beetle showing the way.
Try this
Hold your thumb half over the end of a squeezy water bottle and squeeze in short, sharp bursts instead of one long squirt. Notice how the pulsing spray throws the water further and finer. That pulsing is the beetle's trick — lots of small bursts beat one weak dribble.
Curriculum links
States of matter — mixing liquids, heating and gases
Two liquids mix, react and heat up to make a hot gassy spray — a dramatic example of materials changing when they are mixed and heated.
Explore this on the site: Year 4: States of matter
Evolution and inheritance — adaptation for defence
An extraordinary defence adaptation: the beetle's chemical spray is a body feature shaped to help it survive, fitting the Year 6 idea of adaptation to an environment and its dangers.
Explore this on the site: Year 6: Evolution and inheritance