Summary: Not all spiders weave a web to trap their prey. Crab spiders use camouflage to blend in with their surroundings and long front legs to grab prey that wanders too close.
Pesticides are not needed to control the beneficial Crab spider, but if you feel you need a product because these spiders are a nusiance, I recommend Onslaught insecticide. It's long lasting and covers a broad spectrum of insects.
Crab spiders are so called because they resemble miniature marine crabs. They have wide, flat bodies and their front two pairs of legs are large and held out to the side of their bodies, reminiscent of crabs. They also move sideways or backwards more easily than forwards, also similar to many crabs.
The Crab spider is very small spiders, the largest being only about an inch long, and the smallest are less than a centimeter long. They are very common and widely distributed everywhere on the planet other than the coldest mountaintops, the driest deserts, the north and south poles, and the oceans.
All Crab spiders are predators and active hunters, meaning that they do not build webs, but must catch their prey. Some species are called wandering crab spiders because they seek out their prey by wandering around. Most crab spiders stay stationary, however, and use camouflage to blend in with their background. For this reason, the crab spider may be one of many different colors, depending upon where it lives.
Many crab spiders are called flower spiders because they lurk on flower petals waiting for insects like bees and flies that feed on nectar to fly close enough to grab with their large front legs. They have fast acting venom that immobilizes their prey, so they grab with the legs and then immediately deliver the incapacitating bite. They can capture insects two or three times their size. Crab spiders do not wrap their victims in silk, but begin feeding right away.
Crab spiders are considered beneficial bugs because they capture many insect pest species like flies and mites that are a nuisance to people. They also eat some beneficial insects like honeybees, but their pest diet greatly outweighs the good insects they eat.
Crab spiders can be quite beautiful. The goldenrod crab spider is completely yellow when sitting on a goldenrod flower or sunflower, but can change its color to white when on a daisy. Its body is white, but the spider can produce a yellow liquid pigment in its skin when on a yellow flower to become nearly invisible. It can then excrete the pigment to return to a white color. It takes the spider twice as long to produce yellow pigment and turn yellow than it does for it to turn white. Other Crab spiders resemble tree bark, leaves, fruit, and even bird droppings. Another group of fascinating crab spiders has adapted to look like ants, presumably so they can get closer to their ant prey without being noticed.
Crab spiders can bite, yet never seek out humans. They will run from people or drop off of flower petals to avoid us. Their bite is not dangerous to people, and is not particularly painful, but they should not be picked up with bare hands. If you find one indoors the best way to get rid of it is to place a cup over it, slide a piece of paper under the cup and move the spider outdoors.