Beetling About with Australian Bombardier Beetles

The Australian Bombardier Beetle is a rarely seen largish black and yellow ground beetle. It occurs on floodplains and riverbanks in most of northern Australia and is relatively common in eastern NSW. Until today I’ve only seen these beetles alive in flood refuse and that’s only because the flood was over the bridge to the house I was staying in with a beetlologist colleague – so there was nothing better to do but poke through the flood debris, while being especially wary of snakes. We were looking for something else and didn’t collect them.

The species in our area is formally named Pheropsophus verticalis. Today I came across about 10 of them, so I thought I’d test their bombardierness.

The bombardier was a soldier who put the ammunition in a piece of artillery. The ammunition was then blasted out, to bombard the enemy. When disturbed, bombardier beetles blast out a hot gas, which badly affects the lungs of vertebrate predators. There is an audible puff and small cloud of whitish vapour from the back end of one of these beetles.

I have to say I didn’t do any homework on this, but I should have. I didn’t let my head get near but I did poke one with my finger – the gas was instant and hot and I’ve now got a strange brown stain on my fingertip.

The chemical mix is a hydroquinone and hydrogen peroxide and it rapidly produces heat, to almost 100°C, and the gas benzoquinone. Benzoquinone stains skin brown and may cause necrosis of the skin. I’m hoping I’m OK!

The result for the beetle is usually a dead or seriously incapacitated predator. We tried and failed to photograph the puff of gas. Each beetle produced about four puffs, but the cloud vaporised almost instantly and was delivered while on the move – and the beetles moved rapidly.

If you do find any bombardier beetles, I recommend not handling them.

Some good photos of Pheropsophus verticalis here