Crab spiders get their name from their widely-splayed and elongated first two pairs of legs, which they use to catch prey bigger than they are. They do not build webs but wander around and hunt, often in flowers. Wrestling with prey several times their size can damage the spider — this one is missing a couple legs in the back. With time, the spider can regrow those damaged limbs.
Mecaphesa celer females actually also come in a brilliant yellow variety, although the males have roughly the same color pattern as the pictured female. The “dead giveaway”, according to bugguide.net, that this is celer instead of another Mecaphesa is the four spots on her abdomen which form a trapezoid with the largest side toward the spider’s head.
Swift crab spiders are largely nocturnal and solitary, coming together only for mating. The best line in the article I read on them: “Males do not provide any parental care, as they may be cannibalized after mating.”
Alternative Latin name, for the adventurous: Misumenops celer.