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!