Dangle Leaf Season

The Dangle Leaf season is upon us! 

At this time of year, Emperor larvae change colour, quit their feeding leaves, and go walkabout prior to conking out for five months, normally by a bud or in a fork.

Crucially, they have silked their feeding / seat leaves on assiduously. The leaf petiole join then breaks, leaving the vacated leaves dangling on thin strands of silk, for an indeterminate while.

'Dangle Leaf' can be a highly effective way of discovering Emperor larvae, and a very useful survey technique; but it's rather like Floo Powder in Harry Potter...

First instar feed leaf dangles can be rather indistinct, and can be imitated by some moth larvae, and dangles on narrow-leaved sallows are particularly small; but occasionally you find clusters of first & second instar feed leaves, like these:-

or these:-

More usually, you find a vacated dangling part-eaten leaf like this:-

Most distinctive of all are the third instar feed leaves:-

This one's wrapped itself around the stem:- 

Note the broken petiole and the silk. That's iris, no one else does that (though spider silk can at times throw you). 

Dangles can also contain bits of leaf stalks, which have been silked on too:-

Note the silk on the stem:-

Dangles on narrow-leaved sallows last longer, but are smaller and easily missed.

Dangles on broad-leaved sallows are easier to spot, but get blown off by gales and washed off by rain - though some in sheltered spots may persist long into the winter. 

Dangles last better on sallows in the most sheltered spots, such as in gullies or on the edges of young conifer plantations.

The technique is to wander the woods on a day of good light with a gentle breeze, covering as many sallow stands as possible, and look for leaves - single or multi - spinning around madly in the air. Then home in on the 'pillar, which may be a few centimetres away, or a few metres distant. I carry a 2m long shepherd's crook. 

It's rather like dry fly fishing for specimen Brown Trout on a chalk stream: a lot of wandering and intense observation, the last thing you do is cast. 

There's a but coming up, and here it is: But there are early leaf-fall sallows, mainstream leaf-fall sallows and late-fall sallows (into early December), with much depending on when the first frosts arrive and sallow foliage health.

So, you have to do repeat-visits, checking regularly over a three week period. Sallows that have dropped 50-75% of their leaves are best, and ignore any that are still fully green (until later). Timing is everything.

This year the main Dangle Leaf season will probably run from November 11th to early December, but it may last till Christmas. Much depends on prevailing weather (don't venture out dangling after a storm, go before).

Enjoy... but beware of false prophets (many will come in my name): spider silk can sometimes generate Emperor-like dangles, Geometer moth larvae often silk-up small, usually uneaten leaves, and beware of broken stems. 

Halloween!

 Hibernating PE Cattie with a scary skull marking, from Knepp during the 2016-17 winter (it was last seen ascending a sallow as a big L4 larva on May Day). 

Pet Rescue!

Great to find and rescue two Emperor larvae on a recently fallen sallow yesterday - a tall broad-leaved sallow with 8m of trunk before any branches, which had crashed down over a busy ride and was destined for the chop (someone had already started).

It took the three of us an hour to search.

This shows, 1) that 3rd instar larvae do not fall off when their tree falls - such is the power of their silk pads; 2) that there may be a reasonable number of larvae high up, out of normal reach.  

I have a very good record of finding larvae on recently-fallen sallows...

All told, we saw 8 larvae yesterday: 2 in hibernation (one on a leaf, which is unusual, one on a bud), 2 almost fully coloured-up prior to hibernation, and the other 4 starting to think about it.  

The Dangle Leaf season will get going properly in about a week's time - we need a long dry and calm spell... Sallow foliage is lasting late this year, in the absence of frost - though sallows badly afflicted by Willow Rust have gone into early senescence (explaining the larvae found in hibernation yesterday). Watch this space...

Early Hibernation?

This 'pillar yesterday, Sat October 19th, was fully coloured up (complete with bronze V) and in pre-hibernation pose - about to quit the leaf for bud or stem (unless it had decided to hibernate on that terminal leaf).

Crucially, it had little choice as its sallow tree was 99% bare due to the ravages of Melampsora Willow Rust. How it had fed up to a decent hibernation size on such a depleted tree only the Good Lord knows...

Here's it's tree - 

For the record, the earliest dates I've recorded larvae in hibernation are 17/10/2010, 21/10/2016 and 23/10/2009 - all on early leaf-fall sallows.

 

Knepp 2024

Here's the data from the Purple Emperor transect at Knepp, which runs for 2km down an oak-lined green lane bordered by sallow thickets. It's a single species transect (ignoring all other species), which is walked once a week during the PE season, in afternoons only (from about 12.20), in decent weather (wind is a problem at Knepp), when males are on territory and, crucially, has a massive recording box, and takes about 3 hours:-  

 

This is good data. The UKBMS data is restricted to the standard 5m recording box and largely records males feeding on dog poo. 

The Knepp data suggests that PE had an 'average' year in 2025. However, counts during Week 1 and Week 2 were relatively high. Indeed, the 2024 Week 2 tally was the second highest for that week in the whole data set, only bettered by Week 2 of the 2018 annus mirabilis. 

What happened in 2024 is that the butterfly got systematically blasted away by spells of foul and abusive weather after Week 2. The Week 3 count was way below what it should have been. This is largely because the numpties insist in roosting in sprays in the oak tops, rather than on the leeward side of limbs... Had the weather not broken the annual total would have been in the region of 150-160.

Below are the PE season start and end dates at Knepp. Again, this is seriously good data, derived from diligent recording. This site is very well monitored.

First & Last Sightings at Knepp  2014 - 2024

        (earliest & latest dates in bold)

        2014    18th June     31st July

        2015    30th June     >21st July

        2016    27th June    3rd Aug

        2017    15th June    25th July

        2018    17th June    26th July

        2019    25th July    31st July

        2020    13th June  23rd July

        2021    2nd July     19th Aug

        2022    16th June    29th July

        2023    20th June    25th July

        2024    17th June    1st Aug

Just note how early PE starts there in this modern era, and ignore what the books say. Sooner rather than later a May iris will be recorded at Knepp...  

Only 2021 was a traditional year, with old-fashioned start and end dates.

Also note that PE has only been recorded in August during three of the 11 years.

Purple Emperor pages are being updated on the Knepp websites. 

  

 

  

 

Mid-October Doings

Purple Emperor larvae continue to be unusually scarce just about everywhere this autumn. All bar one recorder (Ben Greenaway) is struggling to find any.

Savernake is going to record its poorest autumn larval count in 16 years of diligent, standardised effort. This is primarily due to:- 

1  A shortage of the younger sallow growth that the females favour (i.e. trees or young branches off mature trees which are just becoming mature enough to flower). This is a problem currently peculiar to Savernake, which is experiencing a lack of sallow regeneration (in part due to squirrel damage - bark stripping, in part due to a break in continuity of ride widening).

2  Coarse foliage, caused by sallows coming into leaf early this year, after a mild winter. First instar larva can't cope with thick leaves. This is a problem everywhere this year.

3  The ravages of rampant Willow Rust, which has rendered many broad-leaved sallows seemingly unsuitable (+ Tar Spot). This is even worse around Swindon and Cirencester, but all but absent in S Warwicks & S Worcs.

4  But, clearly, the 'egg lay' was very low, at least low down.  

However, there is a scatter of larvae around. I was amazed to be shown one on a young sallow rendered 95% bare by the ravages of Melampsora Willow Rust - the small tree on the left, with my gold shepherd's crook. The finder, co-worker Gary Tucker, is looking at the bigger tree - 

That 'pillar is starting to colour up - 

It's not just Emperor larvae that are scarce on the sallows this autumn. Other sallow invertebrates are perhaps even scarcer: I'm scarcely finding any moth larvae, though some moth species may have finished for the season; Sallow Flea Beetles are decidedly rare; I haven't found a single sallow sawfly larva all autumn; the normally common cabbage-like galls of the midge Rabdophaga rosaria are rare, and even the tiny galls that normally abound on narrow-leaved sallows are generally absent; and I've hardly found any Dicranopalpus harvestmen spiders... In fact, the Purple Emperor is actually faring relatively well!!!

Fingers crossed that yet again this the best of all possible butterflies will show itself capable of out-manoeuvring all the nonsenses that gets thrown at it... 

 

Sallow Foliage Conditions...

Purple Emperor larvae remain seriously scarce this autumn: on Saturday, three of us found two larvae in some 15 hours of foliage searching in Savernake. One larva had only just changed into the 3rd instar - its old head was lying close by; that's late.  

Tony Kasiske reports a similar scarcity in Germany, again due mainly to poor flight season weather.  

Interesting to find a sizeable and healthy-looking larva on a branch heavily infected by Melampsora Willow Rust, note the feeding marks -

Most of Savernake's sallows are in poor condition for larvae, with Willow Rust, Sallow Mildew and Tar Spot. Worse, everywhere, sallows came into leaf unusually early, following the mild winter; this means that the leaves were unsuitably thick and coarse by the time first instar larvae were feeding. It may be that a lot of L1 larvae failed, but we wont know as most egg case bases got washed out by heavy rains. 

One again, iris has got to outmanoeuvre a lot of problems if it is to fly in numbers next summer; but don't underestimate him - for a start, it's likely that tit predation of hibernating larvae will be relatively low this coming winter.  

Here's what one of my favourite sallows in Savernake looked like on Saturday, with white mildew on a lower bough, sparse and thick-leaved foliage and a lot of Willow Rust (plus squirrel damage, back right).  We didn't find anything on it -

And here's what a healthy, suitable sallow should look like in Sept - 

complete with damsel not in distress...