Crab Spiders do not build webs to catch prey. This species of Crab Spider (female shown) is born white but can camouflage itself by changing color to match flower or plant colors. It waits for unsuspecting insects to land and gather nectar and then it pounces on the prey.
The name "Crab Spider" was evidently given because of the way it moves sideways and because of the crablike feature of it's appendages.
From Natural Treasures At Pleasant Grove Park - Fluvanna County, Virginia - Screen Shots Are Prohibited