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Your source for information on spiders

Crab Spider      Family Thomisidae & Family Philodromidae

Crab Spider, any member of several families of free-living spiders that resemble small crabs. Crab spiders have short, wide, flattened bodies. The first two or three pairs of legs are longer than the rest and are normally held out from the sides of the body as a crab would hold its claws. Some crab spiders can walk forward, backward, or sideways like fiddler crabs. Worldwide there are about 2000 known species of crab spiders, 200 of which occur in North America.

Most crab spiders are less than 1 cm (0.4 in) in length, although the giant crab spider may reach 2.5 cm (1.0 in). Crab spiders do not spin webs to trap prey, but hunt on the open ground or on vegetation or flowers. In this, they resemble other free-living spiders such as jumping spiders and wolf spiders. Unlike other free-living spiders, however, all of a crab spider's eyes are small and serve primarily as motion detectors. Typical crab spiders are predators that lie in wait to ambush their prey. Though their chelicerae, or jaws, are rather small and slender, many crab spiders possess potent venoms that quickly immobilize their prey. Flower spiders, a particular type of crab spider, rest on flowers and remain motionless for long periods of time with their front two pairs of legs extended in readiness. They ambush butterflies, bees, flies, and other flower visitors; their venoms enable them to successfully attack insects much larger than themselves. They do not wrap their prey in silk after biting, but instead remain with the immobilized prey until they have sucked it dry.

In keeping with their ambush style of attack, many crab spiders are well camouflaged, blending in with their backgrounds. Some resemble tree bark, leaves, or fruits; others appear to mimic bird droppings. Some of the flower spiders are able to change their color over several days, typically between white and yellow, depending on the color of the flower on which they are resting. A common North American species is the goldenrod spider. The giant cockroach hunter is a warm-climate species which often moves northward on shipments of bananas.


Body is usually less than 1/2-inch in length, but up to one inch in larger species.


The crab spider’s color varies, but most species are brown. Some are brightly colored in yellow, green or even pink, depending on the type of flower they frequent.


Crab spiders are passive hunters that ambush their prey. These spiders wait patiently on plants and flowers for flies, bees, butterflies and other insects to visit, and then they pounce upon the unsuspecting insect.

Crab spiders belong to the Family Thomisidae and are named for their crab-like appearance and movements. Crab spiders have two large, strong front legs that are used to grasp prey. They scuttle sideways with their hind legs, although some species do move like other spiders.

Crab Spider Illustration
Crab Spider

Crab spiders differ from other arachnids in a number of ways, including their feeding habits. Instead of spinning webs to catch prey, crab spiders utilize camouflage. Some crab spiders resemble bird droppings, while others look like fruits, leaves or flowers. Some crab spiders are capable of changing colors entirely.

When prey approaches, the crab spider attacks and administers a poisonous bite. Crab spider venom is potent enough to render large insects immobile. It does not affect humans, although on rare occasions, an individual will experience an allergic reaction to spider venom.

Crab spiders produce eggs within a few weeks after mating. These eggs are deposited into two silken egg sacs, which are joined at the center. However, crab spiders are unlike other spiders in that their eggs are not housed within a web. Females commonly remain near egg sacs in order to protect their young from predators. Hatching time depends on environmental conditions. After spiderlings emerge, they resemble adults. These small spiders undergo a series of molts before becoming mature and fertile. Most crab spider species produce only one generation each year. Their life spans also rarely extend beyond one year.

Crab spiders are not dangerous and are not considered a “home pest.” If you find a single crab spider indoors, you can easily capture and release it. Place a cup over the spider and then slide a piece of paper underneath to trap it within the cup. Turn the cup over while holding the paper tightly over the top. Take the spider outdoors to release it.

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