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Draft cover.  Currently scheduled to be launched on June 11th.  Price not determined yet.

Breeding Tip

At last I've worked out how to prevent captive iris larvae from crawling on to their sleeve: tie a wide band of moss around the branch, just before the neck of the sleeve. Bingo! Problem solved (I've lost a few wintering larvae in the sleeve neck over the years).

There's a hibernating 'pillar in the fork here (rather out of focus). I've only got two this year. I rear a few every year to keep me in contact with the butterfly and to indicate development progress in the wild.  

2020 Purple Emperor Calendar

I haven't posted this year as for family reasons I had to move from Purple Paradise in Switzerland back to what is currently something of a Purple Desert in East Suffolk. But I've been following the season by proxy with interest.

For loyal subjects wishing to keep a note of all those purple-letter days next year or looking for a gift with a difference, I'm reproducing last year's calendar, illustrating all stages of His Majesty with three photos a month, all taken in the month they accompany. If you were kind enough to buy last year's calendar, I hope you were pleased with it. Please note these are the same pictures - I haven't been in a position to take new ones!

For more details and a preview of all months, please see HERE. I'm also selling a Swiss Butterflies calendar, HERE.

Apologies for the shameless plug - but I did make the Purple Emperor calendar specifically for contributors to this site!

Guy

Knepp 2019 PE Data

The Purple Emperor flew for fifty days at Knepp in 2019.  That is, seven weeks and a day - the longest Purple Emperor flight season on record. This means that it had a long, flat peak (as opposed to the normal five day peak season pinnacle). The first was seen on June 25th, the last on August 13th (though it was rare after July 24th).

Monitoring Data

We have two monitoring data sets at Knepp: 1) derived from arduous day counts during the peak season period, when we try to cover as much of the 450ha / 1100 acres as possible, and 2) from the single-species transect down Green Lane. The second is seriously kosher.

Day count data suggests that numbers at Knepp were about one-third of those of 2018, but Neil and I were leading so many guided walk groups that we did not manage to conduct a thorough count in fine weather during the peak season period. I managed two day counts of 108, both of which can be calibrated up to 130 to allow for annoying cloud, and Neil’s peak count was 113. This compared to three day counts of over 300 in 2018 (with a maximum of 388 on July 2^nd, by Neil) and a peak day count of 148 in 2017. 

The Green Lane transect data is far more accurate. It indicates that numbers were half those of 2018. This is a single species transect, walked weekly (for six weeks) during reasonable weather (wind needs to be < Moderate strength), during afternoons when males are on territory, and with a 50m recording box. 

Knepp Green Lane Purple Emperor transect data

	2015	2016	2017	2018	2019
Total Counted	112	61	114	201	102
Peak Count	40	18	34	66	33

It seems that Purple Emperor numbers stood up remarkably well at Knepp in 2019, considering the number of factors impacting against the butterfly* and how poorly it fared elsewhere. This may be because the Knepp population is still building. 

*  2018 had been an annus mirabilis for the Purple Emperor.  However, no rain was recorded at Knepp between 31^st May and 28^th July, and many sallow bushes dropped sub-canopy leaves holding eggs and young larvae. By mid-July the ground beneath most of the young sallow stands was carpeted in fallen leaves. It was inevitable, then, that 2019 was going to see a drop in Purple Emperor numbers, though this was mitigated to some extent by 2018’s profuse egg lay.

The second half of February 2019 was very mild, causing some hibernating larvae to waken and expend valuable energy, long before sallows had started to leaf. Some would have perished. 

Worse, the mild February (and a mild winter in general) led to a population explosion of Umber moths (Mottled Umber and possibly Dotted Border and Scarce Umber). Their larvae feed profusely on sallows during mid- to late May, lacerate the foliage and set Purple Emperor larvae back, or even out-compete them (I'm starting to work on this area of Purple Emperor ecology; it’s crucial, as these moths may well be increasing due to mild winters generated by climate change).

Furthermore, as a result of drought stress, a great many sallows at Knepp Wildland and elsewhere came into leaf unusually late in 2019 – long after Purple Emperor larvae should have begun to feed. Sallows had put their efforts into flowering instead. Indeed, 2019 was a prolific sallow flowering (and seeding) year. Many sallows, particularly the narrow-leaved varieties, did not come into leaf until late May. Purple Emperor larvae on them would have struggled, or died.

Finally, after good weather for larval development during April and May, June saw a lengthy spell of cool wet weather from the 2^nd to the 18^th inclusive, when many Purple Emperor larvae would have been pupating. Evidence suggests that the longer Purple Emperors spend pupating and the longer they're forced to stay in the pupal stage, the fewer of them fly. Predation / mortality seems to be high in the pupal stage.

Fortunately, three factors were in the Purple Emperor’s favour: 1) the profuse egg lay of 2018, 2) a relatively low predation rate on hibernating larvae (by titmice), and 3) fine feeding weather during April and May. Also, flight season weather was good, until late July.   

Autumn Larvae

For the last 11 years I've conducted standardised searches for iris larvae in Savernake Forest, Wiltshire. This year's total is 15, the lowest tally during the 11 years.  

There are several reasons, but the three week wet spell in June, when larvae were pupating, is probably the most important - the longer iris spends pupating and as pupae, the fewer adults fly.  

Now, larvae are starting to colour up prior to hibernation (one at Knepp Wildland is about 80% coloured already). 

They construct silk highways up their seat leaf midrib. This one's done that, and has also constructed a bypass! (Savernake, today) -

Sallow Leaf Mildew is prevalent this autumn. It looks as though iris larvae can consume a fair amount of it without ill effect, like this one (feeding damage, top left) - 

Poor Egg Lay

The 2019 egg lay seems to be extremely poor. I'm struggling to find early autumn larvae in Savernake Forest, and think that this will be by far the poorest year in 11 years of dedicating monitoring there (through standardised counts). I've also struggled in Sussex, though some of my favourite trees there have been felled.

Today, in three hours of actual searching on several favourite trees in Savernake, I found precisely none. However, I found May feeding marks and silk pads from a larva I missed finding last Sept when I searched that tree; then I found the remnants of a pupal case about 2m away (of a male) - 

This is only the second time I've found an old pupal case whilst looking for autumn larvae in Savernake, in well over 400 hours of actual searching.  

For the record, larvae are just going into the third instar now, a little late. Here's an L2 larva - 

1600m up!

Discovered a colony of Purple Emperors in a partially wooded ravine 1575m up on a steep, heavily wooded north-facing slope in the Catalan Pyrenees today. Two of the three seen were feeding on sap oozing from Woolly Thistle heads which have been damaged by weevils and beetles.  

Here's an old male (centre) -

And here's the site, centre, from a distance. The rides in this pine wood were lined with highly suitable-looking sallows but we didn't see any Emperors there, maybe the butterfly simply hasn't found these isolated rides yet.

In the afternoon we watched Lesser Purple Emperor males behaving appallingly - every bit as badly as Purple Emperor males - clashing and chasing, from perching points on birch and sallow along a shady leeward edge (it was quite windy) in 30 Celsius -