Sunday, May 26, 2019

Prospects and Predictions for the 2019 Purple Emperor Season

The first Purple Emperor of 2019 will take to the air at lunchtime on Friday June 14th, somewhere in Sussex or Surrey. An earlier appearance was on the cards but larval progress has been slowed down by cool nights and evenings during May (at one staged a May emergence was a possibility).

This prediction is based on the progress of larvae being followed in the wild (last year my prediction was less than 24 hours out...).  

Most years we get records of odd specimens being seen ridiculously early. These seem to be misidentifications (of White Admirals) or result from specimens bred in captivity, which often emerge early (and are undersized).

Numbers could be exceptionally high, though with some local exceptions. This is because of (1) a high egg lay last year, (2) normal levels of larval losses during the autumn, (3) relatively low losses of hibernating larvae, (4) relatively low losses of early spring larvae.  Much, though, depends on flight season weather.

There will be exceptions, particularly in parts of the South East which were severely droughted last summer.

Numbers will almost certainly be down at Knepp Wildland, I fear significantly. No rain was recorded at Knepp between 31st May and 28th July 2018. As a result, leaves withered on many of the sub-canopy sprays on which most eggs are laid and on which young larvae feed. Also, many of Knepp's sallows have shown signs of severe drought stress this spring, and many more have been attacked by moth larvae (mainly Mottled Umber moth). Similarly stressed sallows have also been noted at Bookham Common, Surrey.

Also, numbers will be down in Fermyn Woods, Northants, where several hundred sallows have been felled during extensive Forestry Commission ride widening work, as part of a Back from the Brink project in liaison with Butterfly Conservation. Hopefully, this will only be a temporary blip. Much depends on what happens, and doesn't happen, next.

Conversely, prospects are extremely good elsewhere, including in Hampshire and Wiltshire. For example, sallows (and Purple Emperor larvae) in Alice Holt Forest were saved by 10mm of thundery rain on Fri July 13th 2018. 

The season will be over by around July 23rd.

Cold nights are forecast for next week. This could induce temperature shock on freshly formed pupae - so watch out for aberrations...

Enjoy your Emperors! This is going to be a cracker...

Tuesday, May 14, 2019

Further Progress

Purple Emperor larvae in Savernake Forest (a 'late' site) are about to change skins for the final time. At this rate, the butterfly will be on the wing there by mid-June, and several days earlier in the warmer South East.  

Here's one from today (14th May) -

I'm off to Sussex tomorrow to look at 'pillars there. Watch this space, you may need to bring your Emperoring hols FORWARD...

Wednesday, May 8, 2019

More Larval Development News

Yesterday, May 7th, Dave Law found a Purple Emperor larva which had just changed into its fifth and final instar, in Bentley Wood, Wilts. That's very early, though I've recorded L5 larvae in the wild as early as May 1st (Knepp Wildland, 2011). Normally, larvae enter the fifth instar (L5) between May 10th and 20th.  

In Savernake Forest on Bank Holiday Monday, all seven larvae I saw were in the 4th instar, L4. Four were in mid-L4 stage, three were in early L4 (just changed skin).  

What this means is that, despite the recent cold spell, the Purple Emperor is still likely to be on the wing unusually early - perhaps around June 7th. It's wet foliage that stops them, not cold, and the recent cold spell has been a cold drought.  

They are likely to put on a big spurt as another anticyclone is set to come over this weekend.  

I'll make my final prediction for D Day (or rather P Day) in just over a week's time, once I know when they're going to pupate (last year I was 20 hours out...).

Here's some pics from Monday -

This one has just changed to L4. The cast skin, which it's worn since Sept, is to the side. They don't eat it.

Here's one resting, unusually, on the stem. 

Spot the caterpillar! 

For the record, I have now seen this butterfly in the wild, in its various life stages, for 120 consecutive months - i.e. ten years (I last suffered an Emperor-less month back in May 2009). If you're thinking of taking this record on, seek medical help...