Feather lice and the birds they crawl on are in a constant battle. The lice eat dead skin and bits of feathers, and the birds fight back by killing
lice as they preen. But the lice have evolved a defense: camouflage. Scientists picked 26 pairs of related bird species of different colors, like the
sulfur-crested cockatoo and the yellow-tailed black cockatoo, and used Photoshop to analyze lice associated with each species. Body lice almost always
matched the host's color, as in the insets above: the species of louse that lives on the sulfur-crested cockatoo is camouflaged against its white
feather, and the black louse disappears against the dark cockatoo's feather. That's a good strategy, considering that birds pick these lice off with
their beaks and could spot the bugs easily if they stood out, the authors will report in the
October issue of The American Naturalist. But head lice were always dark, suggesting there hadn't been any pressure on them to blend
in—probably because birds preen their heads by scratching with their feet and thus don't get a good look at the bugs.
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