Crab spiders capture prey by sitting quietly on vegetation and waiting for an insect or other spider to pass by. Then, they simply grab and bite it. Moths and butterflies make up the bulk of their prey. Here, the spider is on a flowerhead of rough blazing star, Liatris aspera
. You can tell by the flowerhead’s bracts, which are rounded, somewhat pouched or swollen, and have thin, whitish or transparent margins that are unevenly torn-looking.