Bombardier beetle (Brachinus crepitans)
The bombardier beetle is famous for its remarkable explosive defence system, in which a volatile liquid is ejected from the anus with an audible popping sound. Indeed, the specific part of the Latin name for this species, crepitans, derives from the Latin for ‘crackle’, and refers to this noise . The head, thorax and legs are reddish-yellow, and the hard wing-cases, or ‘elytra' are bluish-green.
This beetle is usually seen in May and June; the details of the life-cycle of this species are not fully understood, but it is thought that the larvae are external parasites on the pupae of other species of beetle, particularly those of the ground beetle Amara convexiuscula and a staphylinid beetle, Ocypus ater .
The pulses of volatile liquid that are expelled from this beetle when it is threatened are released from the anus and aimed at potential predators. The liquid is produced explosively when the contents of two glands mix in a chamber known as ‘the firing chamber’. One gland contains hydrogen peroxide, the other contains hydroquinone; enzymes are then added. The resulting liquid contains irritant chemicals known as p-benzoquinones, and is released at 100°C ; it causes a sensation of burning if it comes into contact with skin.
The defence mechanism of the bombardier beetle has been the subject of debate between evolutionary biologists and creationists; some creationists claim that this species is too complex and specialised to have evolved, but there are reasonable evolutionary explanations for the mechanism .
