Many moth species spend the day resting on tree trunks, where they can be remarkably difficult to spot. Their camouflage comprises a number of aspects, including matching the background colour (crypsis) and using disruptive patterns that make it harder to distinguish the moth's outline. Not surprisingly, such techniques have been used by the military to hide personnel and weapons. Their history is examined in an exhibition running at the Imperial War Museum in London until 18 November 2007, and in a well-illustrated book, Camouflage by Tim Newark (Thames & Hudson, 2007), that accompanies the exhibition.

The military turned to two main sources of expertise in developing camouflage: professional artists and biologists. Military camouflage was rarely used until the First World War, when specialist camouflage units set up by the French employed artists as 'camoufleurs'.

Artists have also contributed to the study of camouflage in nature. The American artist Abbott H. Thayer, best known for his paintings of idealized women and angels in the late nineteenth century, made several contributions to the subject, including the introduction of disruptive patterning. However, like many people with good ideas, his claims for their applications tended to be exaggerated. He famously argued, for example, that flamingos are cryptic against sunsets, whereas in reality their dark silhouettes are clearly visible. A better idea led to the painting of Second World War warships with bold disruptive designs.

Credit: D. E. SCHERMAN/LEE MILLER ARCHIVES, WWW.LEEMILLER.CO.UK

Whereas Thayer believed that only artists had the necessary insight to understand camouflage, British zoologist and artist Hugh B. Cott — whose 1940 book Adaptive Coloration in Animals was the definitive text on animal coloration at the time — was equally convinced that science was key. Cott advised the British military on camouflage during the Second World War and was critical of the way artists dominated military camouflage. In turn, many artists and military officers considered Cott's recommendations impractical. The Germans apparently agreed with Cott's critics. While working in North Africa, Cott had fake tank shadows painted on the desert surface to fool enemy air reconnaissance. The Germans are reported to have amused themselves by dropping a fake wooden bomb on Cott's non-existent tanks.

The ideas of crypsis and disruption are illustrated in this nude photograph of photographer Lee Miller, taken by David Scherman. Her body has been covered with 'camouflage cream' the better to match the background. The vegetation and camouflage netting is designed to partly disrupt the easily recognizable human outline — and preserve a modicum of modesty. Miller's partner, the British surrealist painter Roland Penrose, taught camouflage techniques in the Second World War and used this photograph to enliven his lectures to the British Home Guard (a volunteer homeland defence force). Penrose also wrote a short instructional book that used examples of camouflage drawn from biology.

The idea of crypsis in biology seems simple but there are complications. Imagine Miller's naked body laid out on the white sands of a coral beach. Her natural skin tones would stand out less than the dark camouflage cream used in the photograph. Any animal that closely matches the colour of one part of its environment may be restricted in other, differently coloured, places where its camouflage will fail. The evolutionary implications of this have formed part of my own research, especially regarding the conditions under which an organism should closely match one part of its environment, or when it should evolve more generalized camouflage. Moreover, disentangling the effects of disruptive patterns from simple crypsis still challenges experimentalists, as lots of organisms, including many moths, are both cryptic and disruptively patterned.

The importance of disruptive patterns has also troubled the military. After the Second World War, the British and US military largely abandoned the idea of disruptive battledress — whose value, they felt, was not supported by the evidence — for cheaper, plain uniforms. Vietnam changed this, as the experience of jungle warfare and an often well-camouflaged enemy convinced the Americans of the value of disruptive patterns.