Bark Crab Spider - Araneae thomisidae xysticus
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Bark Crab Spider

Photo Details
December 13, 2004 - Draper, Salt Lake County, Utah - ©Nicky Davis

Family tree
Araneae thomisidae xysticus

Spiders of this family have a distinct crab-like appearance. Legs I and II are much longer and stouter than legs III and IV. Legs I and II are held out to the sides and project forward while legs III and lay backward against the body. Body hairs are simple and erect. Lateral eyes are elevated on tuburcles. Xysticus species come in various shades of brown and gray, and frequently bear white or yellow markings.  Body is compact, broad, and wider than it is high. There are two claws on each tarsus. Males ( around .10 inch) are smaller than females (around .40 inch) Colors and markings are quite variable within species. Before mating the female is offered a present and secured by some silk threads. These threads are so tiny that it does not fasten her for real but she pretends it does. Crab spiders do not spin webs. They are wandering predators that secure prey by stealth and ambush. They are crab like in motion, moving sideways, backwards, or forward.  Females guard egg sacks, but normally die before spiderlings hatch. Some species are capable of changing color to match their surroundings (over a period of days.  They tend to be forest dwelling, living on and under loose bark, under leaves and stones on the forest floor, and on low lying vegetation.