Elsewhere in this gallery there is a shot of the beautiful black, red and white nymphs of the oak hopper -- this is the adult. I angled this shot to show the peculiar and beautifully pattern horn that is found on some oak hoppers. Many have a rounded head and lack the horn.
These nymphs are about 4-5mm long and clustered on an oak twig. They are surprisingly difficult to spot given their bright colors.