Yesterday, Mon 18th, in heatwave conditions, Purple Emperors took the morning off at Knepp (three sightings only) but became nicely active just before noon, before conking out in the mid-afternoon heat after 3pm.
Then, they put on a good evening flight, from 6pm until after 8pm.
This is classic late season heatwave behaviour. The males have all but given up sallow searching, now the females are all out, wedded and bedded, and are busy egging. Males now go straight into oak territory behaviour mode, though they do a little oak edging and general exploring, and change territories quite a bit.
I watched three females - mature ladies - visiting small sap bleeds on oaks yesterday, one at 1.40 and two during the evening. Here they are -
Those were all 25-35' up in old oaks. The final photo was taken at 8pm. Shortly afterwards, a hornet landed on her, and she flew off in a huff, and went to roost in the top of a hazel.