Am. Nat. doi:10.1086/656269 (2010)

Bird lice reduce their chances of being picked off by their hosts by evolving to match the colour of the birds' feathers.

Camouflage has been well documented in predator–prey relationships. Sarah Bush and her colleagues at the University of Utah in Salt Lake City now report that the same evolutionary trend exists between parasites and their hosts.

By comparing lice from species of dark- and light-coloured birds (pictured), the researchers found that 'feather' lice — which live on a bird's body — match the colour of their host's plumage (insets). However, 'head' lice do not necessarily blend in. This suggests that bird preening drives lice-colour evolution: birds cannot see or groom their heads, so there is no selective pressure for head lice to be camouflaged.