Platycotis vittata (Oak Treehopper).
Size: approx. 9 mm. Photo: 04/08/15, 9 pm.

I am so excited about this photo. It shows a beautiful Oak Treehopper which I found on our outside window frame. The horn of this species can have different lengths and be even absent. The wing patterns vary widely and the body color can be green, mottled or speckled with orange (see second specimen below, 12/24/18). It lives on deciduous and evergreen oaks but causes essentially no damage to the trees. Larva and adults aggregate on twigs into groups of up to 100. Females appear to exhibit protective behavior. Click here for a higher resolution photo. 

bug guide (these photos):