Science Fair Project Encyclopedia
The true crab spiders are a group of spiders constituting the family Thomisidae or thomisids. Thomisids are non-web-building ambush predators whose coloration often matches the substrates they are found upon. They are called crab spiders because of their first two pairs of legs, which are held out to the side giving them a crab-like appearance. These are termed laterigrade legs.
True crab spiders differ from philodromid crab spiders in usually having numerous hair-like setae on their bodies and in having the first pair of legs the longest. Philodromid crab spiders have scale-like setae and the second pair of legs is usually the longest. True crab spiders include the flower spiders in the genera Misumena, Misumenops, and Misumenoides in North America, as well as the nominate Thomisius in the Old World. The bark and ground-dwelling genus Xysticus is widespread in distribution, with many species in North America. Members of the strange genus Tmarus looks much like a small knot on a branch. Other odd thomisids include those that live in carnivorous pitcher plants and those that appear to mimic orchid flowers.
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