Camouflage of predatory crab spiders on flowers and the colour perception of bees (Aranida : Thomisidae/Hymenoptera : Apidae)

The crab spider species Misumena vatia (Clerck 1757) can match its colour t o the flowers it preys on. It can reversibly change between the colours whi te and yellow. For the first time, the spectral reflectance functions (incl uding the ultraviolet) of such spiders are measured, and compared with the flowers on which they wait for prey. The bee-subjective similarity of the p redators with their flowers is assessed using a model of colour vision for bees. While spiders are well matched to white flowers, the colour similarit y between spiders and yellow flowers is not perfect. The UV-absorbing spide rs often present themselves on UV-reflecting yellow flowers. From longer di stances or for smaller flowers, however, bees may use only their green rece ptors, and spiders may therefore be well camouflaged. Also, spiders do not necessarily catch insects on the very flowers on which they sit; they somet imes move rapidly within respective infloresences.