It hasn't sunk in yet - I mean, Hulme and Oates's triple hundred at Knepp, albeit it in a ten hour marathon. We saw a mere six females, so the emergence is by no means at peak. They may, though, shoot over fast in this heat (as they did in 1976).
Our marathon included walking the Knepp Green Lane PE transect, along which Emperors (narrowly) outscored Meadow Browns...
I reiterate Neil's statement about the potential for this butterfly: it's not a rarity, it doesn't want to be a rarity, and it doesn't need to be a rarity - it's just horribly suppressed by the two Fs, farming and forestry, which loathe the sallows it needs. It's not a woodland butterfly, let alone a species of ancient woodland: it's a species of scrub, both rural and urban - but everyone hates scrub (foresters, farmers, and nature conservationists).
One point about yesterday: we didn't see a single Emperor on the ground, the ten or so we saw feeding we all feeding on small sap bleeds on oaks -