Purple hairstreak underside. Purple hairsteaks are the only hairstreak with an orange spot on the hindwing. This species is fairly common in oak woodlands but hardly ever spotted. To find them, you need to go out to a woodland in mid to late July and stare up at the canopy. Any small, silvery butterfly whirling around in the tree tops is likely to be a purple hairstreak. They rarely come down to the ground alhtough this individual above made a habit of landing on the banana leaves in the butterfly garden.