Good News!

Purple Emperor larvae have slowed right down, so the prospects of a late May start to the flight season are receding fast - though we are still on for an early June kick off, with everything depending on the weather over the next few weeks.

Cool nights have slowed them right down, making them miss out on their evening feed. Also, the East and North-East winds of late April stopped them feeding - PE larvae hate wind - and made several larvae change position. Many larvae spent the best part of a week changing skins to the 4th instar (L4).

Here's a mid-L4 larva - 

There are a lot of Willow Sawfly Euura viduata larvae feeding on the sallows at present. They can mimic PE feeding damage. Beware. Here's one -

Onward! We are still heading towards an early and potentially very good PE season (depending on the weather...).

 

Held up!

Emperor larvae have only made slow progress this last week, despite the fine weather - they've been held up by cool nights (and cool evenings, missing out on their evening feed).

Yesterday, of 19 larvae seen in Savernake Forest, only 8 were in the 4th instar (L4); the rest (bar one retard) were skin changing to L4. The most advanced were halfway through the 4th instar (I was hoping to find one skin changing to L5).  

It seems that they've got held up skin changing to L4, as has my captive larva (who spent 5 days changing). 

This means that the prospect of a May Emperor have receded, but everything depends upon the weather... We are still on for an early flight season...

Here's a nice mid-L4 larva from yesterday -

Also, I was pleased to find the leaf beetle Gonioctena viminalis yesterday. The first time I've found this distinctive beetle. It's called the Willow Leaf Beetle, but certainly isn't at all common on the Emperor's woodland sallows - 

 

Spring of 2026

Purple Emperor larvae are continuing to develop ahead of any accepted norms... 

They got held up a bit by a cool and showery week in mid-April, but are set to romp ahead this week, under a strong anticyclone.

Over the weekend of April 18th-19th, 49 larvae were checked in Savernake Forest. Of these, two had recently changed to the 4th instar (L4), but the majority were changing skin. That's early, but not unprecedentedly so. 

Crucially, the sallow foliage is shooting ahead, and caterpillars tend to be in sync with their foliage (White-letter Hairstreak larvae are developing apace).

PE Larvae can race through the 4th instar, in fair weather, though they then take much longer in the 5th and final instar - and they can get stuck at red traffic lights (or a full motorway closure) at any stage, in wet weather. 

Here's an Early L4 larva -

Here's an L3 larva about to shed the skin its worn since last September, and has wintered in. Note the hunched position - 

In late April, Purple Emperor larval feeding 'damage' is fairly distinctive. They feed only at leaf edges, and do not make holes (that's moth feeding). The only thing you can confuse PE feeding with at this time of year is the feeding of the common Willow Nematine sawfly Euura viduata -

The 'record' for the earliest wild 5th instar PE larvae is May 1st (2011). That record is under serious threat this year. 

I repeat that PE larvae have come through the winter remarkably well, and that 2026 has the makings of an astoundingly good Purple Emperor year - unless the weather misbehaves.

Also, again and yet again, this butterfly could be on the wing exceptionally early this year.

Watch this space...  We are living through very exciting times...

     

Spring of 1976...

Fifty years ago, the great butterfly season of 1976 was brewing. I was there, big time: having had the previous eight summers wrecked by the examination system*, I took a self-funded sabbatical, and butterflyed on over a hundred days between mid-April and early September – playing cricket on most of the others. This was low budget stuff, my main form of transport was a three-speed bicycle – and the tarmac melted. I was living near Selborne in East Hampshire, a top butterfly hotspot, but thought nothing of cycling to Chiddingfold Forest. Crucially, I kept detailed diaries.

The previous summer had been hot and dry, and 1974 had been reasonable too. Butterfly populations were on a high. Truly great butterfly summers are the second or, better, third in a sequence of hot summers. ’76 was the third. Incidentally, we have not had a hot summer sequence this century...

The 1976 butterfly season did not begin unduly early, like modern seasons. Here’s some first and last dates, from the Selborne & Alice Holt Forest district:-

Orange Tip                     April 16^th        June 12^th

Speckled Wood              April 19^th            -

Green-veined White       April 20^th       June 18^th

Dingy Skipper                 May 6^th         June 22^nd

Duke of Burgundy          May 7^th          June 10^th

Pearl-bordered Frit         May 6^th          June 6^th  

Small Pearl-bordered      May 23^rd       June 24^th

 

Those are typical start and end dates for central southern England from that era. Butterflies, that summer, didn’t start emerging early until the start of June. Then, Large Skipper commenced on June 1^st and Meadow Brown on the 2^nd (my earliest Meadow Brown of the 20^th century).

The Holly Blue was staging one of its periodic revivals, having been scarce since 1970. The Pearl-bordered Fritillary had an astounding year, with colonies in most young conifer plantations (there were at least ten colonies in Alice Holt Forest that summer, and the butterfly truly abounded in Chiddingfold Forest). 

But Butterfly of the Spring / early Summer 1976 was the Wall Brown, which was almost omni-present – not just on the downs and grassy heaths, but in open woodland rides, along road verges and on garden banks. My diaries record some 250 Wall Browns, between May 10^th and June 18^th, but I didn’t diarise roadside and garden sightings. I saw over 50 in Lodge Inclosure of Alice Holt Forest on May 23^rd. This abundance occurred after a massive 3^rd brood during the sublime autumn of 1975, blowing a hole in the theory that a 3^rd brood depletes populations and is responsible for the current decline. Common Blue and Small Copper were comparably numerous.

The spring weather wasn’t too extreme. April was dry and merely pleasant, and May started and ended rather poorly, though it included a couple of strong anticyclones. The heat and the drought were to come later. This meant that spring butterflies were not unduly stressed, laid a lot of eggs, and had lengthy flight seasons. It was also a great time for larval development. All the while, the Purple Emperor season was brewing...

Next Time: June & July '76.

*Rant: why oh why didn’t we reset the academic year during the Covid pandemic, so that exams take place in the autumn, and we allow our young folk to experience spring and early summer? Rant over.

Ministerial Statement

Here is a Ministerial Statement on the State of the Nation's Caterpillars (Rhopalocera):-

'Led, as ever, by His Imperial Majesty, the Emperor of the Woods,  the High Spirit of the Midsummer Trees, The One of Whom the Nightingale Sings - to cite a few of His numerous epithets - the larvae of some of our butterflies are unusually advanced.'

'Purple Emperor larvae had commenced feeding in Savernake Forest, Wilts, by March 18th, equalling or narrowly beating the record set in 2019 and 2020.' 

'Moreover, the sallow foliage is now unprecedently advanced, following a mild winter (our last cold spell was at the start of January) and the mid-March anticyclone.  Sallow blossom is currently at peak.'   

'Also in the woods, some White Admiral larvae are already feeding, some Pearl-bordered Fritillary larvae have reached their final instar, and if you want something utterly barking, look at the advanced state of White-letter Hairstreak larvae - they're likely to be on the wing in early May.'

'At this range, unless the weather deteriorates, the Purple Emperor is likely to be out by early June, breaking the long-established record set in 1893. Numbers could be astoundingly high, as larvae have come through the winter well.'  

Some Emperor larvae have been feeding by 'bud biting', like this (Savernake 18th March 2026):- 

Most, though, are lined up alongside sallow buds, waiting for leaf buds to loosen, or sepals to darken and open, so they can commence feeding. They are well greened up, like this:-

Watch this space, and get very worked up...

 

The New £20 Note...

We are pleased to announce the new Royal Mint £20 note, with an Emperor as Monarch...

Meanwhile, Purple Emperor larvae are getting ready to start feeding. Many are greening up next to flower or leaf buds. Their first meals will be on loosening buds, by 'bud-biting', or on darkening sepals (they wont feed on very pale, 'anaemic' sepals). 

In general, Emperor larvae are decidedly advanced - as is the spring of 2026. It is quite possible that a few larvae have already had their first post-hibernation meals in the warm South East.  

That's remarkable, as it was only a couple of years ago that the first-ever March meals were detected, at the very end of the month. Now we're heading for a mid-March feeding start. 

We may be heading for a Very Early Flight Season... Watch this space.

On The Move!

The current mild spell hasn't just woken hibernating butterflies, like the Brimstone and Red Admiral, but Emperor caterpillars.

Emperor catties are now waking on mass, and are relocating themselves to align alongside swelling sallow buds. A surprising number of them have hibernated in forks and on twig scars this winter, some distance from the buds. We don't know why. 

It is, of course, unusual for them to waken this early, and they're going to get stuck in the caterpillar equivalent of the dreaded airport Departures lounge for ages, waiting for the sallow leaf buds to start to open.

This is a hazardous time for them, as they can be picked off by predators, birds especially, when moving. Here's one moving up-stem, yesterday, a journey of at least 2m (he's just above the upper fork) -

Also, many are greening up, early, like this one below - 

Watch this space...

 

The 1970s

Here are the known start and end dates for Emperor seasons between 1975 - 1980 in and around Alice Holt Forest, East Hampshire. This is quite accurate data.

Year        First Sighting        Last Sighting        

1975        5th July                   2nd Aug        

1976        25th June                17th July                 

1977        23rd July                11th Aug                 

1978        15th July                13th Aug

1979        17th July                18th Aug                  

1980        20th July                25th Aug                  

What's interesting - beside the obvious fact that most of those seasons didn't start before mid-July - is how short most were.  

This is because most seasons were curtailed by either extreme heat (1976) or by adverse weather events (in 1977, the adults were knocked out by very cold nights at the start of August; in 1978, they were knocked out by a returning Polar Maritime depression). 

Times have changed...

 

 

Fingers Crossed...

 

Emperor larvae seem to be surviving their five month long winter hibernation period relatively well. 

Over the weekend, three of us checked 56 hibernating larvae in Savernake Forest, finding 47. Losing just nine out of 56 during the January and early February period isn't too bad - in fact, it's almost as good as it gets...

At this stage, it looks as though winter predation is only going to be in the Modest bracket, and not High. However, February and early March is the main period for losses. So, fingers crossed...

Some larvae, like the one above, are starting to green up. Now, that's early, very early, but this has so far been a very mild winter. Also, two had moved, up to buds.

If (underlined and italicised) winter losses remain in the Modest bracket and if (ditto) the weather is fine during the crucial pupation and pupal periods, 2026 could (ditto) see a sizeable Purple Emperor emergence - the two key stage periods of loss which seem to determine adult numbers are 1) winter and 2) pupation / pupal time (+ flight season weather, of course).  

Watch this space. We're not there yet, but we seem to be heading there... 

All things are for the best with this the best of all possible butterflies.

Long Hot Summer of '76 No 2: The iris Season...

 

The 1976 Purple Emperor season was one of the greatest of the 20^th century, building on good seasons in 1974 and, especially, 1975. However, it was an unusually short season, with numbers nosediving after three heady heatwave weeks – as was the case in 2025.

Indeed, the similarities in adult behaviour between the 1976 and 2025 flight seasons are immense. 

Nationally, the first male of ’76 was seen at Bookham Common, Surrey, by leading Emperorphile KJ Willmott on June 24^th. That equaled the record earliest appearance listed by IRP Heslop, though Heslop’s diligent searches through the entomological literature had somehow missed the incredible summer of 1893, when the butterfly was ‘well out’ in the New Forest ‘by early June’ and a male was taken by a Marlborough College boy on June 10^th.

The ’76 season, like that of 2025, was dominated by heatwave conditions. Indeed, 1976 brought what was then the UK’s warmest June on record. From June 24^th till July 8^th (inclusive), heatwave conditions prevailed: the temperature reached or exceeded 32C somewhere in southern England for 15 consecutive days. Tarmacked roads melted – I know, I was on a bicycle. 

For the record, there was extensive rain in the Purple Empire on June 19^th-20^th; thereafter rain fell in much of the Empire on July 9^th, 13^th, 16^th and 20^th, some of it thundery. Thereafter, there was virtually no rain until the weather broke at the end of August – and many sallows wilted, along with veteran beeches. The drought had, though, started way back in the spring of 1975. Then, after a hot dry summer, the autumn and winter rains failed – in stark contrast to the autumn and winter of 2024-25 (and indeed 25-26).

All this meant that there was little if any moisture for midsummer butterflies fifty years ago. In early July ‘76 Emperors, of both sexes, descended to the parched rides in early morning (8.30-9.30) to probe for moisture amongst the grasses, accompanied by numerous Purple Hairstreaks. This phase, though, lasted barely a week.

In those days there was little if any dog poo on the rides, as most Emperor woods discouraged public access – you had to hold an Access Permit to enter many Forestry Commission woods. 

Instead, there was a super-abundance of ‘honeydew’, the sticky secretion of aphids. During the midsummer heatwave, the oaks literally dripped with it: Emperors, Purple Hairstreaks and, curiously, Meadow Browns feasted on it high up. Also, Emperors, as in 2025, sought oak sap ardently – and even human sweat: I had a male feed on me on June 29^th, and later watched a pair feeding together on creosote!

In Alice Holt Forest, E Hants, where I was centred, the first White Admiral and Silver-washed Fritillary appeared only on June 21^st, and the first Emperor on the 25^th. I noted the first definite Empress on July 1^st. By July 6^th, they were busily egg-laying – selecting heavily shaded isolated sprays beneath the main sallow canopy. 

On July 10^th, I watched a female ab. lugenda (‘semi-iole’ in the language of the day), at 9.40 and again at 1.30. She was seen once more, in the same sallow glade, on July 14^th. 

On July 11^th I watched a courtship flight, which quickly became a treetop mating that lasted for 3 hours 35 minutes (and must have been the female’s second mating, for she was distinctly worn). 

Suddenly, around July 12^th numbers plummeted, and they were gone. I saw my last on July 18^th, and thereafter concentrated on finding eggs (which hatched fast in the heat) and larvae.

That summer saw a resurgence of old-fashioned butterfly collecting – grown men in shorts, running around with nets. Iris, as it then then called was the main target species. Nets clashed at the few well-known localities, notably Lodge Inclosure of Alice Holt Forest, Kingspark Wood (then FC) in Chiddingfold Forest, and Hell Coppice & Shabbington Wood in Bernwood Forest, Bucks/Oxon. That summer also saw the birth of butterfly photography. 

On several occasions I encountered the legendary Baron Charles de Worms, Heslop’s closest ally. At one stage he was dressed in a string vest, Boy Scout shorts straight out of the Baden Powell era, and corps boots – he was rubbing rancid Danish Blue cheese into a gatepost, as a bait for iris. We shared an entomological friend, a retired GP, Dr John Holmes. de Worms was a delightful man, but it was impossible to get any locality information out of him, and he shed little light on Heslop, my boyhood hero.    

The good news is that those of us who lived through the 2025 Purple Emperor season have a pretty good idea of what the 1976 season was like. 

What matters now, of course, is what the 2026 Emperor season will be like. Watch this space, for one of these years iris will be on the wing in May…

Long Hot Summer of '76, 50 years on: No 1

'If you could walk through Paradise, as if in a dream, and be handed a flower as proof that you were truly there; and if, on waking, you found that flower in your hand - Aye! and what then?'  

(ST Coleridge, paraphrased and modernised, and probably in a Class A illegal state of mind...).

Perhaps those of us who butterflyed through 1976 can answer that...

This is a precursor of a number of posts on this Blog, detailing the butterfly explosion of 1976. Watch this space...

  

 

Masters of the Cryptic Arts

Most Emperor larvae master the cryptic arts whilst in hibernation, displaying chameleon-like capability. 

Here's 'Hermione', s/he was out on sync with her/his background when s/he entered hibernation in early November. This photo was taken on Nov 13th, showing her/him/it/Us/Preciousss as a mottled grey-green larva:-

Here's the same larva on Jan 10th 2026, now perfectly matching the stem background -

Conversely, 'Harry' (photoed 10/1/26) hasn't quite got it right -

  

Happy New Year

from Britain's premier butterfly. 

Here's a 'pillar hibernating in the frozen wastes of Gloucestershire on January 6th - 

 And here's another close by. See if you can spot him...

Butterfly of the Year 2025

Though it will come as no surprise, we are delighted to announce that the Purple Emperor Apatura iris L. has won Butterfly of the Year 2025, stormed it in fact.

Commiserations to the likes of the Large White, Comma, Peacock and Brown Argus, Common Blue and Small Copper, who might have won had the Emperor been less wondrous.  

Here's an unusually dark-form larva in a twig fork in a veteran sallow in Savernake Forest, Wiltshire, signing the old year off -

2026 is of course the 50th anniversary of the Long Hot Summer of 1976. Make no mistake, it's coming back...

 

Mid-December News

Purple Emperor larvae are now all in hibernation. The last lingerers went into hibernation at the start of December - very (and possibly unprecedentedly) late...

Some larvae changed position during mild weather in early December, mainly from buds to forks or scars.  

The sallow leaves are all off too. It looked as though many sallows were going to retain leaves well into December, but there was a mass sallow leaf fall during the month's second week.  

This means that the Dangle Leaf season is effectively over, apart from in sheltered stream gullies and on sallows along the edges of thicket-stage conifer blocks. 

Provisional analysis suggests that relatively few larvae are hibernating by buds this winter, and that forks and twig scars are being favoured, like these two (Savernake, 14th December) -

This is odd.

Titmouse numbers seem ominously high in the Emperor woods this winter, following a successful breeding season in the fine spring weather. Great Tit, in particular, is a major predator of hibernating Emperor larvae. I have already heard my first Great Tit of next year singing (Dec 14th)!

The Purple Emperor has, of course, won Butterfly of the Year 2025, by a very long way. The issue is who has come second and third?

 

 

Lingering Late...

Purple Emperor larvae are lingering late this autumn, as are the sallow leaves. 

This photo was taken in Savernake Forest on Sunday November 30th. It shows a larva still in its October resting position on a leaf tip -

This is the UK's latest recorded observation of a PE larva still on a feeding leaf and not either in hibernation or crawling off to hibernation. 

Incredibly, this larva was feeding here into early November. It is  unprecedented for larvae to be feeding in November (I observed three larvae feeding at the start of November this year). 

Also, a number of larvae have recently changed hibernation position, mainly from buds to forks or twig scars. This happens in mild autumns, usually when larvae feel over-exposed.  

Here's one neatly hidden in a twig scar, taken on Nov 30th - 

And here's one by a bud, again photoed on Nov 30th (note the green sallow leaf background) -

This was a very mild (if wet) autumn, with the first frosts not arriving in The Empire until the night of Nov 17-18th. Many sallows have stayed decidedly green, like this one photoed in NW Wiltshire on Nov 27th -

Some sallows may still be in green leaf at Christmas! Or even perhaps at New Year...

This has impacted on the Dangle Leaf season. In particular, many feeding leaves used in October are still attached by the petiole, meaning that they are not dangling prominently on silk strands. They may or may not dangle now, but there's a chance that some new dangles may yet appear, perhaps as late as Christmas. Much depends on the weather...

PE Distribution Map 1960-2025

 Here's a still photo of Martin Partridge's map of PE records 1960-2025, derived from BC / UKBMS data. Much of Norfolk is mysteriously missing from the video version previously published (with apols to Martin and Norfolk)!  

Autumn Larvae in Savernake Forest

For the last seventeen years standardised counts of autumn larvae have been conducted in Savernake Forest, Wiltshire. Here's the data - 

 

The table shows that autumn larval numbers mostly bumble along at a low ebb, but erupt spectacularly in good summers. These eruptions are highlighted in purple. 2025 was one of them.  It may well have been better than the data suggest, so don't take the data too literally - it merely shows trends.

The work is based on the assumption that the females lay a comparable percentage of eggs within reach each year, though there is no actual evidence for this either way... (searching is done from the ground only, using a shepherd's crook and binoculars - anything else would require a risk assessment the size of War and Peace). 

What's missing here is annual assessment of the quantity and quality of the sallow resource. These are not easy to quantify, particularly foliage quality (e.g. many of the Forest's sallows were afflicted by Melampsora Willow Rust during the wet summers of 2023 and 2024). 

Suffice it that the number of sallows in the Forest fluctuates considerably but is generally in decline, due to increasing squirrel damage ('bark stripping'), ride trimming (which renders many sallows unsearchable by removing lower limbs) and random felling during timber harvesting. 

Also, Savernake is not on particularly 'sallowiferous' soils, lying mainly on Clay with Flints of varying thickness overlying chalk. There has a paucity of sallow regeneration since the early 2000s.  

Remarkable Changes in iris distribution since 1960

This video makes clear how distribution has changed over the last sixty-five years, illustrating how much more of England is now "Purple"!

Mapped by Martin Partridge in Yorkshire. 

Best Dangle Leaf + 'pillar Photo Ever!

Check this out! Definitive photo of an Emperor cattie in hibernation by a bud, with the old feeding leaves dangling close by. 

Congrats to Mark Tutton for taking this photo, in Straits Inclosure, Alice Holt Forest, Hampshire, 11/11/25.   

 

PS 1) that catterpillar will change colour to match its background, and may well move position in this mild weather; 2) those dangles will soon blow or wash off!