I've seen these only twice. Both times, they landed on twigs on the trail and weren't really close to any plants. I'm amazed at how many bees simply plop down while I'm walking, many landing in sand. (That's part of the reason I thought a bluish bee was a bembicine wasp in a recent post.)

(Written a little later) Just reviewed my past posts which included one "plunker" as described above, plus several on mustard. I'll keep looking.

I saw one or two of these today on rocks lining a flower bed at Riley Wilderness Park. The one(s) in question would touch down on a rock, take off, fly several feet, then repeat the action. Didn't see any feeding this time, either.

It was alone, rotating from a small, flat, grey rock to a small bunch of low mustard plants. It was definitely feeding there, touching down briefly on one blossom, then another. After about five flowers, it would return briefly to the rock for several touch-and-go landings there.

A couple hundred feet away was a group, engaged in courtship behavior. The touch-and-goes were chiefly on a light grey concrete curb. A bush sunflower plant was adjacent, but I saw no feeding.