A woody shrub with heads of tiny white flowers. There are often, but not always, larger, sterile flowers surrounding the flower head. The leaves are opposite and toothed, with a distinctive white underside that give the plant its common name.
Rocky outcrops and streamsides.
The insect in the last photo is a yellowjacket hover fly (Milesia virginiensis). More pictures of that bee mimic fly are here: http://www.projectnoah.org/spottings/178....