So you thought this was a good Purple Emperor season? Certainly, the Emperors were blessed with much fine weather, which might mean that activity levels were very high.
However, that doesn't necessarily mean that actual adult numbers were unusually high. In fact, numbers of the Knepp Wildlands transect (established in 2014) were comparable to 2015, which seems to have been a 'reasonably good' year... Peak day counts in 2015 and 2017 were around 36 (36, on a single transect, you ask! Yes, 36, along a two hour route).
I've been carrying out standardized counts of eggs and late summer / autumn larvae in and around Savernake Forest since 2009, by ground searching with a shepherd's crook. The methodology doesn't keep to the same route, but tracks new breeding grounds as they develop and abandons old ones as they degenerate, and involves 40 hours of searching annually. It is based on the assumption that the females lay the same percentage of eggs low down each year (there's no evidence either way).
I am about two-thirds of the way through this year's monitoring, and think the final tally will be in the region of 26-28. That's an improvement on last year's nadir but is certainly not a bumper year - and iris does have bumper years. Here's the data -
The only other person I know of who counts / monitors / surveys eggs &larvae is Brother Dennis (who likes to be known as The Setaceous Hebrew Character - being hirsute, Jewish and characterful. The original Setaceous Hebrew Character was, of course, the Baron de Worms, Heslop's great friend).
Dennis is struggling to find any this year in 'Bucks Best Wood' - a privately owned wood which the enlightened owner manages with iris strongly in mind, and is choked with sallow.
I am also struggling to find larvae at Knepp...
Any other information?