Thomisus onustus is a crab spider species in the genus Thomisus and it has a Palearctic distribution . This species shows an extreme sexual dimorphism both in size and coloration, also in comparison with other crab spiders. The adult males reach a body length of only 2–4 millimetres, while females are 7–10 millimetres long. In males the basic colour of the prosoma varies from yellow brown to dark brown, the opisthosoma may be yellow and green or brown. Also females are very variable in colour, their basic colour can be white, yellow or pink. As a matter of fact these crab-spiders hide themselves adapting the colour of their body to the colour of the flowers on which they are waiting for preys, a behaviour that conceal them from predators and from the pollinating preys. Mating takes place mainly in June. The male climbs onto the back of the female to copulate. Finally, the male leaves the female. The female during the entire mating is completely passive and does not show any aggressive behaviour.
Location: Dorset Heathland
Photographer: B Williams