Wednesday, April 17, 2024

Early Season Warning!

I know this sounds silly, after such a miserably wet winter and early spring, but the Purple Emperor is likely to be on the wing ridiculously early this year, quite possibly at the end of May...

Larvae came out of hibernation and commenced feeding unusually early, having suffered only relatively low predation rates.

Fourth instar larvae were recorded in Sussex in early April. That's unprecedented. Fourth instar was recorded in Notts, at the northern end of the known Empire, in mid-April.  

Purple Emperor larvae can shoot through the 4th instar, when the weather's dry - and a big anticyclone is (at last) setting in...

Of course, cold and/or wet weather can slow 5th instar larvae right down, but if the May weather behaves, expect this butterfly to be flying by its end, or at the very start of June.

Watch this space!


Tuesday, April 2, 2024

And They're Off!

Purple Emperor larvae have begun feeding unprecedentedly early.  Some in West Sussex were probably feeding in mid-March, and certainly during the three days of balmy weather around the Spring Equinox.

Some larvae were also feeding before the end of March in Oxfordshire and Wiltshire, and probably in Nottinghamshire too.  

These first meals were through 'bud biting' - eating the tip of a loosening leaf bud, usually the terminal bud. This is a new phenomenon, something PE larvae have only started doing these last five years or so - seemingly in response to sallows leafing earlier at the back end of mild winters.  

Here's 'Jadis Queen of Charn', photoed near Lambourn, Oxon, on April 1st. The bud tip has clearly been bitten - 

and here's a well-bitten leaf bud, photoed in Savernake Forest, Wilts, on March 25th -

This suggests that 2024 could see an unusually early PE season, but only if it stops raining (larvae can get stuck for ages skin changing and, especially, pupating in wet weather)...

The other big news is that Winter Bird Predation Rates were Unusually Low, despite high populations of Great Tit and Blue Tit, the assumed main avian predators. We don't have the final figures yet, but it looks as though losses were only in the region of 50% - and some of those were to other causes, this larva here had probably been sucked by a predatory invertebrate -

Fingers crossed, but 2024 could see a good or even very good PE season, weather permitting. Watch this space...  

Finally, here's a classic PE breeding ground: an East to West ride in the northern part of Sherwood Forest, Notts, photoed on March 19th.  Tall but thinned pines to the south and west provide shade from intense sun and shelter from the wind (for egg-laying females), and most of the sallows are young, just starting to flower fully - 


Tuesday, February 20, 2024

Greening Up...

Iris larvae are greening up, already. Most of the 11 larvae I checked in Savernake yesterday were between 20% and 30% green, two were more like 50%. Here's three of them - 

Normally, they're that green in mid to late March, so they are running about four weeks early - for now.

The forest sallows are less advanced, though many roadside sallows around Swindon and the Cotswold Water Park are well in bloom, males and the later-flowering females. One sallow along the A419 at Kingsdown (which is Purple) on the east edge of Swindon is quite well in leaf - any larvae on it might well be feeding.  

One of these years iris will be on the wing in Brexit Britain before the end of May...

Winter predation levels remain within the 'normal' range.

Sunday, February 4, 2024

2023-24 Winter News...

Purple Emperor larvae are about halfway through their five month hibernation. Most hibernate by buds or in forks.

A few hibernate in scars or on lichenised branches - 

They are quite heavily predated during this period, and this winter seems to be no exception. Great Tit seems to be the main culprit. Certainly, when tit numbers are high, Emperor larvae get clobbered. Heaviest losses occur during the late winter period. So we are just entering the main danger time...

Tit numbers are currently very high (even RSPB Big Garden Birdwatch data suggests this...), despite poor weather during the breeding season last year. Blue and Great Tits are everywhere in the woods, though as yet they are not roaming around in sizeable flocks.

Larval losses seem to be following the normal pattern - I lost two in a week in Savernake at the end of January, to assumed bird predation. All that remains is the vacated silk pad, like this -

In addition, I seem to have lost two to invertebrate predation - some sucking bug, that pierces the larval skin and sucks out the contents. Like this - 

This seems to be a phenomenon of modern mild winters...

Whatever, some larvae will survive and thrive, and we will have a Purple Emperor season during 2024. 

This is my 60th year of butterflying, the Purple Emperor entered my life back in June 1964...  So it's party time...

Also, and more importantly, Notes and Views of the Purple Emperor was published sixty years ago, in 1964.  Here's a photo of the lead author, IRP Heslop, with his 37' 'high net', and his van. 

Tuesday, November 14, 2023

Dangle Leaf Time...

Purple Emperor larvae have been disappointingly scarce this autumn. My annual autumn tally in Savernake Forest, Wiltshire, determined by standardised searches, was a meagre 22 - less than half what I'd expected.  

It now looks that the July weather was too poor for the laying females, and that the egg lay was consequently low - at least away from the East Hampshire, Surrey and West Sussex region where the butterfly enjoyed an annus mirabilis.  

I have yet to find any sign of the insect in my local patch, Cirencester Park Woods, Gloucestershire - in over 50 hours of searching for larvae. This is in part due to the severe outbreak of Melampsora Willow Rust mentioned in my previous post, which has been rampant in the Cirencester / Cotswold Water Park area, but also in part due to poor flight season weather reducing the egg lay in what is a very small population, of recent origin.  

Everything now depends on the Dangle Leaf season. Dangle Leaf is a method for finding PE larvae as autumn merges into winter. 

In brief, during early to mid- autumn, larvae assiduously silk their feeding leaf stems on to branches, before wandering off to find somewhere to hibernate. The petiole join then breaks, only for the leaves to remain attached for a while by silk, dangling or even spinning madly. These dangles are diagnostic of iris, no other insect does this. 

In wet and winter autumns the dangles quickly fall off, especially on larger leaved sallows and along windward edges. Dangle Leaf is therefore about as reliable as Floo Powder in Harry Potter or the Rhythm Method in family planning - but it is quick, picks up larvae just above normal ground-searching level, and can be hugely effective.  

This is Dangle Leaf - 

Those two leaves are attached by silk strands, the hibernating caterpillar is directly above (though most larvae wander further away, and can be found as far off as 3m from their abandoned feeding station).  

The 2023 Dangle Leaf season is running a little late, as most sallow bushes have remained green in the absence of frost (this is a very mild, if horribly wet autumn). But it is kicking off now. 

Weather permitting, the Dangle Leaf season should last from mid-November to the start of December, possibly beyond.

Give it a go, it's insane...

Thursday, September 14, 2023

Egg Lay & Willow Rust: Important News

I'd anticipated that autumn larvae would be fairly numerous this year, but it looks as though I was wrong, again.  Badly. 

Initial searches suggest that the egg lay was low.  Certainly, larvae are hard to find, if not very hard.  It's relatively early days though, as I've been doing other things, but the signs are ominous.

It now seems that the females hadn't got into the swing of laying before the weather deteriorated in early July and, critically, that many of them were blasted away by the St Swithun's Day gale - before they'd laid many eggs...

Worse, far worse: the broader-leaved sallows in some districts have been severely affected by Melampsora Willow Rust.  I've been aware of this rust since 1977 but it's never been too much of a problem, swelling up in wet midsummers, but abating before autumn.  

This year, it's rendered most of the broader-leaved sallows in my home patch (Cirencester Park Woods) wholly unsuitable: many sallows there had dropped most of their leaves before the end of August, others were covered in golden leaves that are destined to drop early.  I haven't found a single larva of any Lepidopteron or sawfly species on infected sallows.  Here's what to look for:

Early Stage Infection -

Then it gets Serious - 

  Then this happens -

That photo was taken on August 21st!  It shows some resprouting, from a largely senescent sallow.  

Here's a leaf underside close up - 

All the broader-leaved sallows, plus the poplars and aspens in the Cotswold Water Park (another study site) are severely affected, but Savernake Forest and Bentley Wood (both recently visited) seem OK.  The pox seems to start at Junction 15 of the M4 (Swindon East).  

Crucially, narrow-leaved sallows (Salix atrocinerea & S. cinerea types / hybrids) seem far less affected. 

PLEASE LET ME KNOW IF YOU COME ACROSS OUTBREAKS OF WILLOW RUST.  We need to gather evidence (I'm liaising with Forest Research's Tree Health Dept. at Alice Holt Forest).  Email me on  

Friday, August 18, 2023

Final sighting

The last Purple Emperor of 2023 was a female seen in Ruislip Woods on August 3rd. This means that there were only three sightings in August: this one, and my two sightings in Savernake Forest on August 1st. 

Perhaps the key point about the 2023 Purple Emperor season is that it arrived earlier than anyone anticipated and caught us with our trousers down... By the time many observers had realised that the butterfly was in fact well out, the weather was deteriorating. The St Swithun's Day gale effectively ended the season at many sites.

Numbers were excellent, if not superb, in central southern England - even in places where sallows were severely affected by drought in July and August 2022, and shed many leaves. This suggests that the Emperor may be becoming drought proof, like the White Admiral.

Elsewhere, numbers were at best modest - but many recorders got out rather too late in the flight season, and the butterfly may have been under-recorded.

Here's the pupal case of a female, who hatched out circa June 30th, in Cirencester Park Woods, Glos, taken on August 14th. The cases can persist for weeks, or months. 

The long journey into the 2024 Purple Emperor season has started. I'm beginning to look for larvae. Watch this space...