Folks. Wild Purple Emperor larvae are unusually well advanced, with early- to mid-final instar larvae present in West Sussex, West Berks and S Glos. White Admiral and White-letter Hairstreak larvae are similarly advanced (I haven't got a reading for Silver-washed Fritillary).
This means that, as things stand, the Purple Emperor is likely to be on the wing in early June, possibly earlier.
However, we've been here before, notably in 2011 when there was a fine early spring. That was followed by a cool May, which slowed things down, and then a wet June. The first Purple Emperor was seen that year on June 13th.
Long range weather forecasting is extremely hard in the UK, but the indications are for a drier than average May, with a warm ending. The middle third of the month, though, is likely to be cool (but dry), which could slow larval development right down. [Info from The Weather Outlook which I find fairly reliable].
Watch this space, but my original prediction for the first Purple Emperor of 2020 was June 11th - but I may well need to bring that forward.
Regarding numbers: much depends on May and June weather, especially the weather when larvae are pupating, and during the pupal period, and of course flight season weather. Winter predation was 'Moderate', as measured. At this range, numbers could well be
quite good or even good.
Finally, I am delighted to announce the discovery of Apatura iris in the Cirencester area, probably as a recent colonist. There is a fair chance of the odd aggressive male beating the living daylights out of the Large Blues on Daneway Banks...