Here are images of crab spiders at the hunt, with some success. The spider sits quietly in a flower, waiting for a foraging insect to venture too close. Then it pounces.
On one lucky day, March 20, 2016, I saw four crab spiders hunting. On Trail 14 near Searsville Lake, a spider lurked on a petal of a chaparral clematis (C. lasiantha, AKA pipestem clematis). Winter ants browsed the flowers, coming close, but apparently not close enough to be caught. I monitored this scene for over two hours, off and on. The spider never moved more than a slight adjustment of its legs; the ants browsed the whole time.
Walking along Trail 14 and up Road E a little, I saw some blue dicks (Dichelostemma capitatum ssp. capitatum). Three flower heads stood together. Each one had a resident crab spider. These spiders moved much more than their cousin down below, but still stayed motionless for minutes. One captured a flying insect, held it for a long time, then appeared to drop it.
A pale swallowtail butterfly (Papilio eurymedon) visited a flower. The resident crab spider made no move.
Nine days later, 3/29, I revisited these three flowers. A crab spider was still there.