|Thomisus onustus on the hunt, camouflaged in yellow by homochromy with an anthemis flower.|
It has a Palearctic distribution from Great Britain and Portugal in the West to Japan in the East. It is present in most countries of Europe, but it is absent in Iceland, Ireland, Norway, Denmark and Finland. North-south distribution extends from Sweden to South Africa and from Siberia to Central Java, including temperate and tropical ecozone.
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 (0.079–0.157 in), while females are 7–10 millimetres (0.28–0.39 in) long. This species is characterized by the prominent rear corners of the opisthosoma.
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.
These spiders prefer warm temperatures, forest-free areas, dry and sandy habitats with high solar radiation and dry grasslands.
Like other species of the family Thomisidae these crab spiders do not make a web, but actively pursue their preys. They usually wait for preys positioned for hunting on flowers. The spiders are disguised by assuming the same colour as the flower, fooling both insect and bird predators. The prey consists of flower-visiting insects of all species, such as hover flies, bees, wasps, butterflies or beetles, which are often several times larger than the spider. They take their preys with two powerful and highly enlarged front leg pairs and usually kill them by biting on the back of their neck. Emerging spiderlings of Thomisus onustus may feed on pollen or nectar when insect preys are lacking.
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.
- Gershom Levy - The life cycle of Thomisus onustus (Thomisidae: Araneae) and outlines for the classification of the life histories of spiders - Journal of Zoology, Volume 160, Issue 4, pages 523–536, April 1970
- Vogelie A.,| Greissl R. - Survival strategies of the crab spider Thomisus onustus Walckenaer 1806 (Chelicerata, Arachnida, Thomisidae) - Oecologia. Vol. 80, no. 4, pp. 513–515. 1989.
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