Beetles warm to heat of the forest

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Most animals flee forest fires - but buprestid beetles seek them out, swarming to them from distances of up to 30 miles away, because they need to lay their eggs in freshly burnt wood.

Scientists had always wondered exactly how the beetles, of the genus Melanophila, were able to detect conflagrations at such a distance. Now, a team at the Friedrich Wilhelms University in Bonn, Germany, has learnt how the beetles are able to function - as heat-seeking missiles. Two organs found in pits beneath their thorax are sensitive to precisely the infra-red wavelengths produced by burning woodlands.

Few animals are able to sense heat directly. Humans detect it through its effect on the skin rather than as an innate sensation; thus chemicals or friction can generate the same "feeling" as warmth. Many snakes have pits near their nose which can detect the heat given off by warm-blooded prey. But the beetles' sensors operate differently. As the scientists found, the beetles "feel" heat as if it were pressure - though a welcome one. Snakes, on the other hand, have nerve fibres that act as true thermoreceptors, and literally "smell" heat.

In the experiments the German team detected activity in the nerves running from the pits in response to an infra-red lamp. Writing today, in the science journal Nature, the scientists said: "This provides the first physiological evidence of an insect infra-red receptor."