These ambush bugs were on a goldenrod. This species is abundant around here at present. I find that once queen anne's lace blooms these bugs become very noticeable. The flowerhead provides them a good place to hide as they can sit below the flower head waiting for insects to land. But they are also common on goldenrod where their yellowish colouration blends in well with the yellow flowers. These bugs are not mating, because when an ambush bug pair mate, the male sits sideways to the female. This pose is sometimes called coupling, and you might see several males riding on the back of the much larger female. Why? Speculation is that it may help them catch bigger prey items.