Possible significance of the red patches of the female crab-spider, Misumena vatia



The female of the crab-spider, Misumena vatia, is one of the few spiders known to be able to change its colour reversibly. Adult females usually have red patches on each side of the abdomen. The most likely insect enemies of Misumena are red-blind, and because the red patches absorb ultraviolet exactly as does the rest of the abdomen the patches are not distinguishable to insects in the ultraviolet. It is suggested that the red patches function as a warning colour for birds and other vertebrates, which are not red-blind.