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Tuesday, 17 August, 1999, 12:25 GMT 13:25 UK
Bull's-eye beetle
Beetle, Eisner and Aneshansley
The spray comes out at 100 C
It is one of nature's hot shots. The African bombardier beetle can turn its heavy artillery in virtually any direction and hit the target with extreme accuracy.

The ammunition is impressive too: A boiling hot, toxic fluid that lets off a loud bang on detonation.

Beetle, Eisner and Aneshansley
Any part of the body can be targeted
These stunning photographs of Stenaptinus insignis were taken by researchers at Cornell University and published in the Proceedings of the National Academy of Sciences. They show in detail one of the most remarkable defence mechanisms in the natural world.

The beetle needs such sophistication because of its vulnerability on the ground. Unlike flies, butterflies, dragonflies and many other insects, the beetle cannot take instantly to the air when under attack from a predator, usually ants.

It has to unfurl its wings first from beneath their covers and the discharable glands buy the creature time to get airborne.

Beetle, Eisner and Aneshansley
Two deflectors are used to direct the spray


The photographs show the beetles curling and revolving their abdominal tips to spray their different body parts and even specific segments of individual appendages that have been pinched or poked with fine-tipped forceps.

Close-up images of females reveal a pair of shield-like deflectors near the opening of the abdominal tip that are used one at a time to control the direction of the spray. Male beetles use a single deflector.

Beetle, Eisner and Aneshansley
The beetle needs time to get airborne
The spray contains p-benzoquinones, compounds well known for their irritant properties.

The precursor chemicals have to be stored separately in the beetle's abdomen because they combine explosively when brought together. This explains how the resulting quinones are ejected at high speed and at such a high temperature (100 C).

Indeed, when all guns are blazing, this creature is literally too hot to handle. This, the researches say, raises an interesting question: If the beetle can target even regions on its own body, how does it withstand the heat and irritation that comes from the spray.

Beetle, Eisner and Aneshansley
The defence mechanism keeps ants at bay


The study was conducted by Thomas Eisner and Daniel Aneshansley.
See also:

28 Jul 99 | Science/Nature
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