Mid August '26: Larval Progress & the State of the Nation's Sallows

These are challenging times for Purple Emperor larvae in the wild, with heatwaves impacting on larval development and the ongoing drought affecting sallows and foliage quality.

In and around Savernake Forest, Wilts, larvae are developing steadily and the sallows are holding up relatively well, for now. 

We have equalled the mid-August record for the earliest 3rd instar larva (set in 2018). All other larvae this last weekend (15th-16th) were in the 2nd instar, mainly in mid-L2 state. 

As yet, there are no signs of larvae developing way ahead of schedule, and threatening to double-brood (and we don't want them to to that anyway, it's a waste of butterflies). 

To date, larval losses have not been severe, or as high as they were this time last year. That may be because the females have laid in deeper shade this year, and/or because the heat may have reduced predator numbers significantly. 

However, here's a dead 2nd instar (L2) larva found there yesterday - 

This individual may have died in the heat, shrivelling up soon after changing skin (as can happen), or it may have been attacked by a predatory sucking bug (the Red-legged Shieldbug, a vicious predator of small caterpillars, has increased phenomenally on sallows in Savernake in recent years). But overall, larval survival is reasonable.  

Here's a nice late L2 larva from yesterday -

Numbers-wise, larvae seem to be locally good in the forest, but distinctly patchy, with some breeding areas being surprisingly neglected - but it's early days in the survey season. 

The problem here is that the Empress is forever moving the goalposts, adopting different laying strategies from year to year, and it takes us a while to crack what she's been doing. Her only consistency is her sublime disregard for our botanical taxonomy - she does not use Clive Stace's New Flora of the British Isles (2019, 4th edition) let alone Meikle, R. 1984. Willows & Poplars of Great Britain & Ireland. Note that the vast majority of sallows I find larvae on key out as hybrids (mostly as x Reichardtii hybrids).  

Some districts have had no effective rain since June 11th (after a very wet start to the month). Wisley, Surrey, has just recorded 60 rainless days. Sallows in free-draining situations are dropping leaves (e.g. Cotswold Water Park [gravels] and on the Lower Greensand). Savernake's sallows are largely holding out well, but for how much longer...?

We need a Ministerial Statement on the State of the Nation's Sallows...

2026 'Egg Lay': 1st Assessment

Big session looking for eggs and larvae in Savernake Forest yesterday, conducting an initial assessment of the 2026 'egg lay' (= number of eggs laid) and of larval survival in the heatwave. A gang of four searched one of the main breeding grounds (ground searching + shepherd's crooks, aiming to follow the larvae through).

Goodish news:- 

1  The 'egg lay' looks good, though it is almost certainly lower than last year (an annus mirabilis in which the Purple Emperor won BC Wiltshire's Butterfly of the Year). 

2  Larval survival seems to be OK-ish (judged by the number of finds of egg case bases + 1st instar silk pads and feeding, minus any live larva). Last year, we lost a lot of baby larvae to heat desiccation, and some eggs 'boiled in the bag'. This year, the females seem to have laid more in heavy shade, sensibly.

We found six 2nd instar larvae, 10 1st instar larvae; only one egg (about to hatch); one dead egg (predated by a sucking bug)) and five 'L1 Fails' (egg case base + pad & feeding - larva [egg case base is abbreviated to ECB, though that also stands for England & Wales Cricket Board; and about to hatch is abbreviated to ATH]). That's good.  

Best, sallow foliage condition was Good to Very Good - heat and drought haven't adversely affected sallow foliage, though a few early-leafing sallows (males mainly) have gone through the phase of being suitable for young larvae.

Here's yesterday's best photo, of a late L1 larva (1st instar) next to an early L2 (2nd instar) -

Silver-washed Fritillary and Purple Hairstreak seemed to be over in the forest - imagine that, paphia and quercus gone by the end of July...

At present, it seems that the UK's final 2026 sighting of Apatura iris was of a female seen by Toby Ludlow in Lincs on Fri July 24th (perspective: July 26th used to be National Purple Emperor Day, usually coinciding with peak season...) - unless some second brood adults emerge in the autumn....

 

A late landing

 

Apropos of nothing, this resilient specimen landed on my arm (Alice Holt, 18 July). It stayed for some time – I was yet to shower that day. I believe this to be a female, can anyone confirm? 

Extra Time, and Penalties...

The 2026 Purple Emperor season (which was at best 'average') bumbles on, way past its sell-by date.

Today, Tues July 21st, 3 females in Chambers Farm Woods, Lincs, and a female on a sap run and, briefly, this old male on territory at Sapperton, Glos -

At Sapperton, the first male was seen on June 21st. The butterfly was only discovered (per larvae) in the district during Lockdown in April 2020, perhaps having colonised during the annus mirabilis of 2018. 

I dread to think how poorly larvae are faring in his desiccating heat, but will find out soon. 

Only one thing can end this heatwave: Bristol Balloon Festival, due in early August...  
 

Going, Going, Gone....

The 2026 Purple Emperor season is stuttering towards its inevitable end. 

Today, Fri 17th July, a female was seen in a wood near Basingstoke, Hants. 

Yesterday, two males were seen on territory at Knepp, Sussex, and this dying male was found on the ground there - 

He had clearly lived life to the full...

In addition, yesterday, one was seen in Lincolnshire and this male was nicely active at Sapperton in Gloucestershire -

However, he was not seen today.

But watch this space, it may be that a small second brood appears this autumn, weather permitting: we already have 2nd instar larvae, by mid-July... 

'In my end is my beginning'.  

Sat July 11th: Season Ending

This photograph of an old male on territory in the 'Dead Beech Glade' in Savernake Forest, Wilts, is probably of my last Purple Emperor of the year. You can just make out a pair of antennae and the front of the forewings - 

It was taken at 2.15pm on Saturday July 11th. Time was when the Emperor season was only just beginning on that date!

All we saw during an exhaustive and exhausting search of Savernake's best territories was this and another faded male, though there must be the odd female still on the wing.  

July 8th: Heatwave Intensifying...

Today brought very difficult weather conditions in which to work Emperors, especially late in the flight season: cloudless, calm and hot from early.

In such conditions, late on in the season, Emperors tend to stick to the vicinity of their feeder trees, which are usually sap bleeds. Sap runs are never easy to find, and can switch on and off from day to day. This year, they have been even scarcer than usual - Patrick's Tree, normally Knepp's No 1 feeder tree, has hardly functioned...

I was in a new part of Savernake today, and quickly learnt that weather conditions weren't right for surveying. The one sap run there, the best I've seen anywhere this year, attracted half a dozen male Red Ads, and briefly this old male Emperor (and it is male, it's completely lost its purple iridescence) -

The signs of an ageing season were everywhere, including this pupal case remnant, from two weeks ago -

and the next generation of larvae is advancing. Here's a late 1st instar larva, soon to change to the 2nd instar, and gain its horns - this early, rather begging the question of whether we'll see some 2nd brood Emperors on the wing this autumn???

Elsewhere, it looks as though the Purple Emperor is over in Alice Holt Forest, Hants, already...