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!  

Dangle Leaf Update

The 2025 Dangle Leaf Season is now underway, though it is being delayed and hampered by unusually mild weather.

The impacts of mild November weather are:- 

1) most broader-leaved sallows remain green, with larvae lingering on the leaves, or being hard to find in hibernation because of the amount of leafage; 

2) in mild weather larvae can wander far and wide whilst seeking a hibernation spot (many wanderers seem to get predated, but this is hard to prove or disprove). 

In Savernake Forest yesterday, one nice broad-leaved sallow was completely bare of leaves and had already gone through the dangle leaf phase, just 2-3 sallows were in prime Dangle Leaf condition (having shed about 75% of their leaves), but the vast majority of broad-leaved sallows were still in green leaf. The narrow-leaved sallows (Rusty Sallow-types mainly) were more advanced, but there aren't many of these in Sav. One narrow-leaved was in prime Dangle Leaf condition, and revealed 5 larvae.  

Of 25 larvae seen, 14 were still on the leaf, though most of these were ready to quit; 10 were in hibernation, by buds or in forks or twig scars; one was wandering about. 

Several more known larvae were listed as Missing In Action, but may yet be found. We also found a few dangles without being able to locate the larva, which had wandered off.

Every autumn I pray for cold weather in early November, to encourage larvae to crawl just a few centimetres from their vacated feeding leaves before conking out... but every early November, it's mild (ridiculously so this year)...

Here's one of yesterday's larvae in hibernation on a twig scar - 

And here's a pair of classic Dangle Leaves, + silk - 

  

A Guide to Dangle Leafing

The 2025 Dangle Leaf Season will shortly start! We used to dread November: not anymore! Bring it on! After the flight season, it's the best time of the Emperoring year.  

'Dangle Leaf' is by far the easiest way of finding any of the immature stages of the Purple Emperor. Indeed, it is often easier than detecting the territorial males. 

Text first, then piccies.  

1  During the autumn, PE larvae strengthen the petiole join of their seat leaf and feeding leaves with copious amounts of silk (after the 1st instar, PE larvae are serial spinners of silk). 

2  Larvae then vacate the browning leaves, and wander off into hibernation (the odd one tries to hibernate on the leaf). 

3  The petiole join then breaks, but the silk prevents the leaf from falling to the ground.

4  Instead, vacated seat leaves and feeding leaves stay attached to the twig stem for an indeterminate period - depending on windiness, rainfall and the amount of silk. 

5  Most 'dangles' last for about a week, but in well-sheltered situations (e.g. stream gullies, sallows along thicket-stage conifer plantations) they can persist for a few weeks. One gale, let alone a named storm, and most blow off.  Very few survive till Christmas.  

6  However, there are 'early', 'mainstream' and 'late' leaf-fall sallows - the latter often staying green into December. Much depends upon the arrival of frost, and the intensity of the summer or autumn (traditionally, in the Purple Empire, the first frost used to occur around Bonfire Night). 

7  The 'early' leaf-fall sallows will be ready for Dangle Leafing very soon.  

8  This year, the main Dangle Leaf period is likely to start in mid-November and end in early December - but much depends on the weather.  

9  The 2025 Dangle Leaf season could be MEGA, because larvae are present in unusually high numbers this autumn (despite high mortality rates amongst young larvae in the July and August heatwaves). 

10  To practise Dangle Leaf, you'll need a hooked stick (ideally a shepherd's crook) and a pair of binoculars, and patience. Those who spent their youth fishing are well placed to go Dangling. 

11  In good light, wander the woods, inspecting sallows which have dropped 50% to 75% of their leaves, looking for bronzed or (usually) deep-brown leaves spinning gently in the breeze. On still days, give the sallow a tap, and watch for spinning leaves. Windy days are difficult, with too much leaf movement.

12  Usually, you'll need 2-3 minutes per tree. This means that Dangle Leafing enables you to cover a lot of ground.

13  But, beware of false prophets: leaves spinning on a thread of brown broken stem, leaves attached by spider silk (rare this autumn) or tangled with white feathers.  

14  A true Dangle Leaf is diagnostic of Apatura iris. No other UK Lepidopteron does this. An experienced Dangler can tick off a new location by merely spotting a good dangle, without finding the larva. 

15  However, the hibernating larva can usually be found within 2m of a Dangle Leaf cluster. Most are aligned alongside middle-sized buds, or in forks. Occasionally, they hunker down in a bark scar. They very rarely venture into fissured bark. Seemingly, many get predated whilst crawling about prior to conking out, so don't worry too much if you can't find the 'pillar (look again in spring).  

16  Ideally, repeat visits over a 2-3 week period, to locate early and late larvae and dangles.

17  Tell nosy parkers you're looking for biodiversity (they'll leave fast).

18  Forget sallow taxonomy, the Empress speaks a different language to our botanists. Sallows which offer(ed) mid-green foliage are favoured.  This autumn, most larvae are on sallows with a shaded south-facing aspect (tall trees to the immediate south).

19  Most larvae and dangles are annoyingly just out of reach! Hence the need for binoculars.

20  Warning. This is addictive.

A classic Dangle Leaf cluster, plus silk - 

Dangles can consist of a single leaf -

These are old feeding leaves, with irisian eating marks - 

Beware of false prophets. This is not iris: far too much silk, and the leaf is uneaten (spider silk probably) - 

A few larvae conk out for a while on their old leaf, then move to a stem later -

Cue dancing dryads, singing -

            "This is Dangle Leaf!  This is Dangle Leaf! 

            Sallow leaves spinning in the autumn breeze...".

Enjoy!

    

UPDATED 3/11/2025  We checked 22 larvae in Savernake on Sun Nov 2nd. Only two were definitely in hibernation, with a third in pre-hibernation (off leaf, but will move again) and a fourth wandering about prior to conking out (NOTE in mild weather, they can wander for hours and for many metres, with many vanishing without trace...). 

Most larvae were nearly fully coloured up, soon to quit the leaf - so they'll be a mass exodus into hibernation there this week.  There's a but coming up...

BUT, only one sallow was ready for Dangle Leaf (ca 75% bare). The vast majority were still very green indeed.

SO, unless we get a sudden frost (the longer range weather forecasts are picking up signs of colder weather from mid-November) the Dangle Leaf Season is likely to start late this year, perhaps peaking in the last week of December.

Watch this space...