Background matching is perhaps the most obvious phenomenon that falls under the label of crypsis. Stevens & Merilaita (2011) describe background matching as situations where ‘the appearance generally matches the colour, lightness and pattern of one (specialized) or several (compromise) background types’. There are fascinating examples of species that behaviourally select their microhabitat and orientation so as to enhance similarity to features of the background, and species that change aspects of their appearance in ways that enhance background matching. The degree of background matching is often imperfect; this is thought to commonly reflect the fact that organisms are viewed against a range of different backgrounds, and so they have evolved appearance traits that offer some degree of matching against several of these. Understanding background matching addresses important issues in evolutionary biology, such as the maintenance of polymorphisms. We discuss how predation rates that depend on the frequency of morphs in the environment may be a common explanation for polymorphic crypsis, and the role search images might play in this process. Achieving highly effective background matching in a complex environment is difficult and this may create room for other types of crypsis.
