The bombardier beetle, or Brachymus creptians, has a “machine gun”. When attacked, it makes an explosive sound and spouts smoke.
This beetle combines chemicals from two separate glands to make the smoke.
The first gland produces a solution of 25% hydrogen peroxide and 10% hydroquinone, while the second gland produces peroxidase, an enzyme that catalyses the reaction. When these solutions are combined and heated to 100°C, smoke and nitric acid vapour is produced and explosively released.
If you put your hand close to a bombardier beetle, it will rapidly release a scalding, noxious, red vapour. This nitric acid will cause blisters on afflicted skin.
Bombardier beetles also know how to aim the tip of its abdomen to target an enemy. Via this method, it can hit a target a few centimetres away. Even if it misses, the explosive sound will scare away any predator.
Normally, bombardier beetles store enough chemicals for three or four shots. However, some entomologists have found that some species can fire up to 24 times in rapid succession if provoked.
As these beetles are a bright orange and silver-blue colour, they are very noticeable. They act as if they do not care if they are seen, as they are equipped with an effective cannon. Generally, beetles with a colourful coat have a unique, ingenious defensive mechanism to ward off curious animals and insects.
Despite this, rats that know that the beetle loves to use this “ingenious defensive mechanism” quickly grab the beetle and plant its abdomen in the ground. After attacking it continuously while in the ground to exhaust the beetle’s rounds, the rat bites off the head first.
(from the Encyclopaedia of Relative and Absolute Knowledge by Bernard Werber)