Possibly milkweed bug nymphs. There is some adult bug on a leaf at the far right side of your photo that actually looks like the rear end of a white-crossed seed bug, but I can't see it too well. Many seed bug nymphs look similar at that stage. Check this site for the milkweed bug nymphs.
http://www.missouribotanicalga...
By the way, the Missouri Botanical Garden has an excellent website for all sorts of gardening-related information.
