Thecla betulae is large for a hairstreak.
   It has brown dorsal wings and small 'tails' protruding from the hindwings.
   Females have a brilliant orange patch in the top corner of each forewing.
   The ventral side wings are a distinctive bright orange, with two white lines streaked across them.
    Though they are large for Hairstreaks, they are little butterflies that are found along hedges, scrub, and wood edges but are often overlooked since they spend so much of their time high in the tree canopy. Like Purple Emperors, this butterfly uses "master trees", usually European ash.  
   Males and unmated females congregate at the tops of isolated trees. Once mated the female descends to lower levels to begin laying her eggs. 
   She lays her eggs on Blackthorn (Prunus spinosa) shoots in late August, and they overwinter, hatching the following spring when the buds are breaking.
   She lays round, white eggs.
   Looking like blackthorn leaves, the older caterpillars are extremely well camouflaged and feed only at night.
   Males rarely descend.
   Both feed mainly on honeydew.  
   Both sexes are dark brown on the dorsal side, with orange tails. The female also has a bright orange band across both forewings. The ventral sides wings are similar in both sexes and are bright orange with wings closed showing orange-brown underwings with two wavy white streaks and small tails. Dorsal sides are brown with an orange mark.
   They often rest with their wings closed showing orange brown ventral wings with two wavy white streaks and small tails. Dorsal side wings are brown with an orange mark.
 
    * This butterfly species is protected in the UK by Schedule 5 of the Wildlife and Countryside Act of 1981.