Xysticus Crab Spiders

Xysticus Crab Spider on Rough Blazing Star

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Xysticus spp.
Family: 
Thomisidae (crab spiders) in the order Araneae (spiders)
Description: 

All crab spiders generally resemble crabs: Their legs extend outward from the sides, and they can walk in any direction. There are several species of crab spiders in the genus Xysticus in Missouri. Generally larger than flower crab spiders, they are usually dull gray and brown and have brown, rusty, tan, white or yellow markings, especially on the abdomen, and they often have a midstripe on top of the carapace (head). The first pair of legs are large and powerful, as in flower crab spiders, and are covered with many tiny spines.

Size: 
Length (not including legs): from 1/4 to 3/8 inch (females); males about 1/8 inch.
Habitat and conservation: 
These spiders can be found under bark and on the forest floor under leaves, rocks and on decaying logs. You can sometimes find them on low fence posts, flowering plants and outbuildings. Woodland crab spiders are not easily seen because of their cryptic coloration but nevertheless are fairly common.
Foods: 
Moths and butterflies make up the bulk of their insect prey. Crab spiders capture prey by sitting quietly and waiting for an insect or other spider to pass by. Then, they simply grab and bite it.
Distribution in Missouri: 
Statewide.
Life cycle: 
As a general rule, spiders in our area hatch from eggs in spring and spend the growing season eating, maturing, mating and laying eggs. Females continue creating egg cases as long as the weather holds out. As temperatures cool in fall, their metabolism slows, and they generally die when it freezes. Egg cases overwinter, and spiderlings hatch in spring.
Human connections: 
It would be easy to dismiss the importance of these tiny predators, but when you consider the many insects whose numbers they help control, you become thankful for this natural, nontoxic "pest exterminator."
Ecosystem connections: 
Spiders help to control populations of the insects they capture. Being small themselves, they easily fall prey to larger predators such as birds, reptiles and mammals. Many animals eat their eggs. Many birds forage on tree bark for species such as this.
Shortened URL
http://mdc.mo.gov/node/6486