Benjamin

[David M]

....14/20 continue on into February….

That's not unreasonable, Ben. Hopefully, now there are a few more insects taking to the air, the pressure will ease slightly on these static 'packed meals'.

I shall look forward to the next update.

[Benjamin]

Thanks both. Overall the situation remains positive but February did indeed deliver the blow I feared.

Jacob’s twig has rebounded.

My depressing run of losing my favourite and the most impressive individual in the stable continues. Becoming attached is a dangerous game!

He was one of only two losses, with John Middleton being the only other whose short journey came to an end in February.

12 from 20 remaining at this stage is better than expected, and if things warm up a bit they could be feeding again by April. But I’m not wishing away this cold spell. After a pretty decent summer and an unusually warm autumn It feels like a solid winter should be welcomed. If we extend this cold spell a little then I’m sure we’ll have a punchy spring with an explosion of activity. As much as I’m looking forward to everything kicking off i’d probably rather wait a little for that, rather than have one of those early stuttering years where nothing knows whether it’s coming or going.

[David M]

Such a shame to lose Jacob, Ben. I guess (like you thought) he was too attractive and plump for his own good.

Here's hoping those that remain can escape predation.

[Benjamin]

I checked in on the WLH eggs on the 17th and was pleased to find that they’d finally hatched (at least a couple of weeks later than last year). I check regularly so knew this must have happened at most a day or two previously.

With the flowers nicely open I could spend a few minutes scanning for movement within and with some good fortune I found a very active little caterpillar checking out his new home.

I’m not sure in which instar they begin to fluoresce under UV but for no good reason I guess it’s probably the second. Anyway I’ll find out over the coming days.

[Padfield]

Hi Benjamin. You're right - they start fluorescing in 2nd instar. I found this chap by night and I'm pretty sure he's 2nd:



Guy

[Benjamin]

Excellent - thanks Guy. Although the current lack of sun in this part of the world appears to be holding back the butterfly season, the otherwise excellent spring weather (warm and wet) has ensured that things are now starting to move along nicely - albeit largely hidden from view.

[Benjamin]

Back to the WLH and things are rattling along nicely. The elm samarae are developing quickly now, but many will be missing the key area, as our little parasitic friend has been busy methodically working his way around and homing in on the nutritious seeds. He looks nicely swollen and must be due for a skin change.

[Benjamin]

I’ve struggled to find time to check on the PE cats recently, but I did finally manage it yesterday. 7 have made it through and all 7 are now feeding.

19/20: 14/47 - 29.8%
20/21: 13/35 - 37.1%
21/22: 12/44 - 27.3%
22/23: 7/20 - 35%

With a relatively small stable this year (I believe because there are fewer caterpillars to be found rather than because I searched any less thoroughly or effectively) I did say I wouldn’t read too much into the data, but it is pleasing to note that the predicted 6/7 have survived and also that with fewer caterpillars survival has edged up as it did in 20/21. For this particular data set 8 survivors would have been the perfect result, as I would expect the year with the fewest caterpillars to return the highest survival rate. But again as already mentioned, once we get down to small numbers the results naturally become less reliable as a single loss can produce a significant swing.

Kerstin lost to sucking insect of some sort

Andrew Man

I will try to spend some time tracking them over the next couple of months but the next big effort will be UV pupae searches in early June.

[Pauline]

Your ongoing research provides a fascinating insight Ben. I look forward to reading about your findings supported by your excellent images.

[David M]

Good to know many of the larvae are still thriving, Ben. I guess late March/early April is a critical time as nesting birds will be at their apogee in terms of foraging for insects (and their early stages).

Hope the pupal hunt is productive.

[Benjamin]

Many thanks Pauline and David.

I popped back a few days ago to see how things were progressing and unfortunately a further two cats have been lost. Leatherlips predated and Agnes Naismith shrivelled/predated. Agnes certainly died waiting by a bud. Whether she ran out of reserves or was attacked by something I’m not sure but given that she had ‘woken up’ and travelled to a bud I think she was most likely in good shape and so predation seems more likely.

Andrew

Agnes R.I.P.

Ursula

So we’re down to five this year! This seems very few, and as I generally seem to lose 60% or so of pupae (and they have a long way to go to get there) I wonder if any emperors will hatch in these woods this year. UV pupae searches generally reveal a few that I have overlooked, but to save the situation I’ll have to hope that this year I’ve missed rather more than in previous years.

But of course all will not be lost regardless of numbers this year. Emperors are so mobile that truly isolated sites probably don’t exist in this part of the country. The habitat is on the verge of improving dramatically at SW and with purple woods all around, and the mighty Knepp only a couple of miles to the south, the reasonable habitat that exists currently and any prime habitat the develops will be exploited by wandering females very quickly.

[Benjamin]

The April 24th series goes on for another year:

2023

Each year so far I have wished that I’d placed some kind of mark on the floor to direct me to the identical spot to take the photo. I still haven’t done it and as a result I spend far too long trying to figure out how to look at last year’s photo on my phone while simultaneously framing this year’s shot also looking at my phone. Impossible obviously, and flicking between apps to try to find a workaround just leads to more frustration. Anyway - I took a picture that’s close enough to see that, well, it’s a bit like it always is. I think this series has run its course

But on a positive, it’s always nice to be in the woods and in this particular spot there are always lots of orange tips and I could also check on PH eggs that have pretty much now all hatched (although this pic is from one I’d taken home to rear in the garden).

[Benjamin]

And to complete this quick-fire attempt to update my diary, I should just mention WLH.
I’ve only been monitoring a couple of cats from eggs but as soon as they start feeding on leaves I will find many more very easily with UV searches.

This one is L2 and has now started to fluoresce under UV. Interestingly he did not fluoresce as an L2 until he started feeding on leaf buds. I think he will soon change into L3.

[Benjamin]

This post is an attempt to detail my current thinking with regards the fluorescence of immature stages and how this phenomenon relates to their ecology.

I’ve made the mistake previously of assuming that if larvae/pupae are fluorescing under UV light then this will make them MORE visible to predators that see well in the UV part of the spectrum. Clearly it’s hard to make this scenario make sense, and I’ve struggled to imagine some kind of benefit that would outweigh this apparent cost. This has led me to consider all kinds of possibilities, some better than others but unfortunately all stemming from that fundamental misunderstanding.

When we go out at night and flood our subjects with UV light, the phenomenon we witness is UV induced visible fluorescence.

Although an extremely useful method for surveying for certain species, the real interest for me is that this practice gives us an insight into what they might be doing with the UV light they receive during the day. A process that is normally hidden from our eyes in daylight is dramatically exposed when UV is isolated from the rest of the spectrum at night.

Although we don’t know how much of the UV is being reflected (I guess we must be able to measure this with some specialist equipment) some of it is certainly being absorbed, and after some molecular excitation (that obviously I don’t understand) it is reflected back as longer wavelengths in the visible part of the spectrum.

It seems pretty well accepted that birds see well in the UV part of the spectrum and quite possibly better in that range than in the visible (to us) part of the spectrum:

https://www.nwf.org/Magazines/National- ... ird-Vision

So although I don’t know much about this subject at all, I like the idea that we might be witnessing a solution to the difficult problem of what to do with UV. UV light can apparently be very harmful to insects, and as a result many have evolved a high degree of UV reflectance. Although this potentially keeps them safe from the harmful effects of UV, it enables predators with good UV vision to home in on them very effectively. By absorbing it in order to then reflect back light outside of the UV range perhaps we are seeing a solution where the harmful effects of absorbing too much UV are avoided, while simultaneously remaining hidden from predators by reducing their UV reflectance.

If that is what’s going on then it’s very neat and makes the UV induced fluorescence we see at night make a lot of sense. In daylight these fluorescing organisms will be melting into their surroundings by reducing the UV signal that would give them away to avian predators.

Unfortunately, however, I can’t really find this spelt out in the literature, which makes me think I must have got something upside down or backwards. The only study I can find that focuses directly on this is one by Czarnecki et al. (2022), and although this produced some interesting results with painted dummy caterpillars, it’s hard to say how well the study mimicked natural conditions. So as usual I’m left trying to make things work without understanding the subject and of course that’s a dangerous game. There seems to be lots of question marks in this area though, so I wouldn’t be too surprised if the conclusion is correct even if all my working out is completely wrong.

Just one final point relating to the literature. The suggestion very often is that the UV induced fluorescence is acting as a warning signal. Just one example from Sourakov (2019):

“Finally, in Asbolis capucinus (Hesperiidae) (Fig. 1D), which is, to my knowledge, not known to be chemically defended, the fluorescence is localized to the last abdominal segment. While in the first three species the fluorescence seems to enhance the aposematic pattern, in A. capucinus the caterpillar inhabits a tube-shaped leaf shelter in a palm leaf, so that the last segment is the one that ‘plugs’ the entrance. In this case, the last segment may therefore have a possible warning pattern that is visible to predators, in the same way that shelter-feeding skipper caterpillars and their pupae frequently have eyespots and other warning patterns, on both ends of caterpillars (Janzen et al., 2010).”

Perhaps this is right, but if the caterpillar in question isn’t chemically defended then i’m not sure how effective this ‘warning’ would be? Surely once the deception is exposed a glowing bum plug (sorry) just becomes an invitation to dine (interesting sentence!). I guess if it’s mimicking a genuinely toxic species then it could work but I don’t think that’s what is being suggested.

It would make more sense to me that rather than acting as a warning the fluorescing final segment that remains on view is actually undergoing some kind of process along the lines that I’m suggesting, and the result is that it reduces its visibility to predators.

Anyway - however much I’ve misunderstood this subject, I’m much more comfortable travelling in this direction. Emperor pupae and hairstreak caterpillars are masters of disguise and the idea that they’ve taken this ability a step further in some way sits much better with me than any interpretation that requires an explanation of the opposite.

[Padfield]

For what it's worth, I had come to a broadly similar conclusion to yours. UV light - especially UVB and UVC (though UVC is almost entirely blocked by the ozone layer) is penetrating, high-energy and potentially very damaging at an intracellular level. Therefore, all organisms seek to block it in one way or another at their surface. Reflecting it directly comes with the risk of alerting birds, who can see it. Absorbing it all at the surface means absorbing a lot of high-energy radiation right at the surface - and maybe overheating the surface if the organism spends a lot of time in the sun. Re-radiating the energy immediately at a lower frequency seems a good solution, and there are plenty of biological (and non-biological) pigments which do this. Like you, I acknowledge I might have quite the wrong end of the stick!

I was concerned when I began using UV that I would be exposing the caterpillars to a risk, but a little research suggested that UVA torches are very much less intense than sunlight.

I wasn't aware of the warning theories. It's not uncommon, though, for features which evolved in one context to be put to another use by ever-ingenious nature.

Guy

[Benjamin]

Thanks Guy - reassuring to know you’re on the same page.

WLH instars seem quite tricky - especially distinguishing between L2 and L3. I think both L2 and L3 can be very variable in terms of colouring, and no doubt this is linked to diet.

I’ve managed to follow this one very closely though, so having checked it regularly while it remained motionless for 4 days, I can be sure that these photos are of a very fresh L3. I would suggest that the photo you posted in my diary earlier Guy, is also a fresh L3.

L2 skin changing

L3

L3

L3

I haven’t started searching for them properly yet, but a little further up the road I couldn’t help but notice a little feeding damage that led me to this individual. This elm is further advanced and I couldn’t find any sign that it had flowered. There may have been some that I’d missed but I imagine this caterpillar has only fed on leaves. Not the clearest picture as I didn’t want to disturb him too much (just lowering the branch had sent him marching towards the leaf base) but he has no sign of any pink/purple and is completely green. He is only slightly larger than the definite L3 so I assume he is in this stage also, but perhaps a day or two older.

[Benjamin]

…….and actually remembering back to some i collected last year it’s clear that they remain very variable in all instars. This is an L4 perfectly matched to the seed clusters I found him hiding amongst. His tree was late to leaf.

[Benjamin]

I’ve been monitoring WLH closely over the last couple of years. UV torch surveys enable a detailed distribution map to be built up with relatively little investment of time - just a few long night time walks each year when the majority of larvae are in their final instar.

The conclusion is perhaps not very surprising. Where there are elms, there are WLH caterpillars. Elms line the streets of Brighton and Hove and feature heavily in the parks and green spaces.

Trees hosting plenty of caterpillars

Concentration of caterpillars is greatest in the wilder areas where elms have low hanging branches and summer nectar sources are abundant. Mature trees in these areas can host up to 20 L4 caterpillars. They tend to favour low hanging branches bordering clearings that receive plenty of sun.

Prime

Street trees, on the other hand, rarely host more than the occasional caterpillar, but having said that it is rare to walk past a run of street elms without at least spotting a few. Where the low hanging branches have been allowed to grow (rather uncommon on busy streets) it becomes much more likely to find a good number of caterpillars. Here is one such example at night:

https://youtube.com/shorts/mUrz_HG3Z-U?feature=share

The picture here is that of a giant colony (in the sense that elms are common enough to be never truly isolated) living on the 17,000 elms that dominate the landscape from the seafront to the downs. I guess as a result of this wide distribution adults are rarely seen in high concentrations, but equally wherever you are during the flight period it is never surprising to encounter one or two - on a showy planter when walking through the centre of town or nectaring in front gardens if you’re meandering along some suburban street.

When I first rented a house in Brighton I monitored caterpillars on an elm that overhung the back garden, and whilst in my next house a caterpillar somehow pupated in my car and hatched when I was out on the road. I didn’t know much about them before moving here (I’d only popped down from London to see adults on the creeping thistles of Hollingbury Park a couple of times) but it hasn’t taken long to develop a real affection for them. They’re fascinating at every stage and to be able to live in the heart of this impressive stronghold has certainly been one of the stand out highlights of the move to this part of the country.

The trees are nearly all now in full leaf and the caterpillars are L4 and just starting to colour up and head off to pupate.

Mid April - mid May

Yellow and green L4 colour forms and others darkening for pupation

[Pauline]

Another interesting report Ben. I believe that Paul Harfield found much the same about the Elms around here. ie. the WLH is very much under recorded and most Elms he monitored showed evidence of WLH. Love the shot demonstrating the colour comparisons.

[David M]

You've done so well to record this, Ben. I can't imagine how much work goes into it.

Thanks for sharing.