Benjamin

[trevor]

More wonderful work Ben! I do wonder with the heatwave and drought this past summer,
how butterfly numbers will be affected next season. I went to Herstmonceux Castle gardens
during the worst of the heat, after the hose pipe ban, and most plants, which are well cared
for, were shrivelled and some desiccated and others had finished flowering early.
When we had the first serious rain after the heatwave the gardens bounced back remarkably,
but had the damage to eggs, larvae etc already been done to some of the high summer species ?

Trevor.

[Wurzel]

Interesting reading as always Ben . What with us experiencing more extremes; hottest summer, coldest winter etc, I'm wondering if this will be beneficial for butterflies especially if we get more snow/ice events?

Have a goodun

Wurzel

[David M]

Looking at the weather maps for the period (I was abroad) it seems that lack of rainfall rather than excessive temperature was the most significant anomaly. This would fit in with the theory of egg desiccation, and as we know iris is particularly fussy when it comes to selecting sheltered spots, often low down in what appear to be relatively humid (close to streams etc) areas we can assume that humidity is a key factor when providing the best conditions for developing eggs.

Sounds eminently plausible, Ben. Temperatures further south in Europe are generally far more excessive than in southern England and yet iris thrives perfectly well. Thunderstorms too are usually much commoner nearer the Med so I guess desiccation is less of an issue.

Interesting to note your comments regarding overwintering positions. I'd love to know what relative predation rates are per region in various countries. It is undeniable that snow cover will better conceal hibernating cats, and I suspect greater bird mortality during such periods will also assist.

[Benjamin]

Thanks for your interest and comments Trevor, Wurzel and David.

As always there are winners and losers when it comes to these weather events. Of course the ability to cope with weather variability is tied to habitat provision, and for many of our species this is where the real issue is to be found.

With the big swing in temperature I just thought I’d get in a few more frosty pics before they seem too out of place…..

[Padfield]

Hi Ben,

Do the wintering cats fluoresce? In winter it is easy for me to check out my old haunts in the dark and still be back home at a sensible time (impossible in summer!). I'm itching to try the UV lamp on iris cats. In my new region, although I've discovered where the sallow is, I haven't yet found unequivocal evidence of iris so I don't know where to turn the torch.

Guy

[Benjamin]

Unfortunately not Guy. I certainly could have saved myself a lot of time if they did! I think in L4 and L5 the head and some of the markings fluoresce quite weakly but they don’t in the earlier instars. I guess whatever eats the pupae would most likely take out the lot if they fluoresced in hibernation.

[David M]

First class images, Ben. It's quite amazing how they survive being freeze-wrapped like that. Iris is a special species, and even more so when you know what they've had to endure in winter to earn the right to fly.

[Benjamin]

Thanks David. PE is certainly a fascinating species to study, but then if you dig deep enough I suspect they all are.

Predation in hibernation over December won’t mean too much as, due to late leaf fall/dangle leaf, most of the stable were only added at some point during that month.

It’s unlikely I’ll add any more now, so I can look at the figures and compare with previous years:

Caterpillars found and monitored in hibernation:

19/20: 47
20/21: 35
21/22: 44
22/23: 20

This next one’s a bit rough as it’s the total number of caterpillar sites located (inc those lost into hibernation, too high to access or with presence only confirmed via definite dangle leaf).

19/20: 56
20/21: 41
21/22: 71
22/23: 26

Survivors (feeding again post hibernation)

19/20: 14/47
20/21: 13/35
21/22: 12/44
22/23: ??/20

Based on these figures I suppose we should expect 6 or 7 to make it. I’ve previously suggested that fewer caterpillars distributed throughout the available habitat would likely result in increased survival. The benefit being imagined here is that of being thinly distributed, and thus avoiding the danger of focus feeding birds. I don’t think there’s any safety in numbers when it comes to remaining undetected in hibernation - quite the opposite is likely true. I wonder how key this is - enough for pre hibernation caterpillars to try to knock each other off the same leaf spray? They’re unlikely to succeed given how effectively the caterpillar prolegs lock into the silken highways they lay before themselves, but they certainly don’t seem to like each other’s company.

Unfortunately however, the small number of caterpillars this year are still somewhat grouped on the best trees. I have three within a metre of each other on one tree and a couple of twos. With such a small sample this could go either way - a big statistical swing one way if their trees are searched, or a big swing the other if they happen to be overlooked. As such I don’t think we need to overthink whatever data results - admittedly difficult to stick to this when spending hours and hours alone with one’s thoughts in the woods.

As always at this time of year it’s worth tracking the colour changes and looking at the fantastic colour range that caterpillars exhibit.

Jacob Distelzweig

Thomas Doughty and Ursula Kemp

Isabella Rigby

Agnes Naismith pretty picture…

And a better shot for highlighting the excellent camouflage

Jacob Distelzweig deserves a special mention. He is this year’s whopper, and is very similar to Sally from last year and, I think, X4 from the year before. Of course we’re only talking mm here but once you become accustomed to the standard size anything unusual stands out a mile, and these extra large individuals seem outrageously bloated. Unfortunately as with the supersized that have gone before him, Jacob is not very well situated and despite his excellent attempt to match his body to the green and his head to the orange of the bud, he will only ever look like a swollen, over-indulged lump placed out as some kind of offering to the tit gods. A bit mean, and hopefully I’m wrong, but I expect the offering to be accepted any day now.

In other activity I’m getting excited by WLH. Most likely less than 8 weeks until eggs begin to hatch. Having searched extensively around Brighton and Hove with my UV torch last year I’ve got a good idea where the best areas are so it’s quite easy to locate eggs.

[Matsukaze]

I'm posting this with some trepidation here, as you know what you're talking about whereas I don't, but if you've got a hibernating PE larval population of something in the range of 50-200, surely that's too low for it to be worth birds specialising in hunting them down? Even if a single individual bird does it, are PE larvae going to amount to a meaningful proportion of what it needs to feed on to survive?

[Benjamin]

Hi Chris -

You’re right and thanks for asking - I always really welcome thoughts/comments.

The population here is certainly too low for any birds to specialise in seeking them out. I think birds will sweep through the trees checking all likely areas for anything that looks like a meal. When searching for PE cats I come across all sorts of other insects/spiders that no doubt get picked off alongside any hibernating cats that are unlucky enough to be discovered.

The danger for the PE cats, at least as I see it, is that as they no doubt constitute rather an excellent treat, any bird that discovers one might be more motivated to check the surrounding area (the rest of the same tree) a little more thoroughly, and with a refocused eye for iris. In this way (and to exaggerate dramatically to make the point) 50 PE cats on a single tree would likely all be predated, whereas 50 PE cats spread evenly across 50 trees will survive much better.

This assumes that the tits will at some point visit all 50 trees in the example, and having spent lots of time in the woods watching them during winter, this wide ranging search does indeed appear to be the way they operate. They will miss many of the single cats alone on their trees, but when they discover the bumper crop in the jackpot tree there will be carnage and nothing will remain.

Obviously a daft example but I guess I’m suggesting that the same effect will occur to an increasing extent as we group the caterpillars and move away from the single caterpillar on a single tree optimal situation.

It’s actually exactly the same when it comes to my own search for hibernating caterpillars. I can be day dreaming my way through the most boring of tasks known to man until I suddenly find my first cat on a new tree and then my focus and enthusiasm comes rushing back before gradually ebbing away again.

[bugboy]

Fascinating stuff as always and I do enjoy reading your thought processes as you work out the why wherefores of what's actually going on in this alien world. I'm in agreement with you in thinking that lower numbers mean a better chance of surviving. With regard to what seems to be the main winter predators (Tits) its worth noting that the average tit is very lucky to reach 2 years old and therefore there's never really much chance of a population of birds learning to focus on them long term. They are mostly learning from scratch each winter so in a good iris year, some individual birds may well become expert iris predators, but come the next winter those predators will have become prey and so the slate has been wiped clean for the next round of hide and seek.

[Matsukaze]

Hi Benjamin - that makes good sense - thanks!

[David M]

Jacob Distelzweig certainly looks at risk, Ben. As you say, given his size he'd be a real bonus find for a predatory bird.

It's always striking to see how much contrast there is between individual larvae. Makes you wonder what evolutionary strategy is at work there. Clearly, they must all provide a reasonable degree of camouflage otherwise certain shades of colour would cease to be represented.

[Benjamin]

Thanks for the input Paul - seems to fit in well with what I think I see in the woods…

Hi David. The striking variety of colours we see in the overwintering larvae is certainly one of the most appealing aspects of the winter search - you never know how the next one will look.

The possibilities are endless because they have the ability to gradually colour match their surroundings. This ability seems to suit iris as it is (at least superficially) appealingly sophisticated, and appears to be a level on from the more basic alternative of simply chucking out a variety of morphs and hoping something sticks (survives). If the latter situation were the case then as you say, you’d no doubt gradually lose the variety (admittedly in this case it’s hard to see how it would exist in the first place) in favour of one or two highly successful colour morphs.

Anyway - they do gradually change colour, and it’s a fascinating process that I’ve tried to document in previous years. They must be able to get some kind of colour read from the substrate they are in contact with, and as the head quite often takes on a different colour from the body, it seems most likely that this ability isn’t tied to their limited eyesight but is a feature of the larval skin. Although not very well studied i guess it’s probably quite common in caterpillars, and is no doubt the same kind of process that leads to the triggering of different colour morphs in pupae. I always see it most strikingly when rearing peacock (dark on the net cage, yelllow on the nettle stem) but of course many other species show similar variety.

It’s nice that it seems more sophisticated in iris though - not so much the triggering of a morph but almost total plasticity. I guess the time frame available is a key difference here. I’m really hoping that one year I get a very green caterpillar lined up next to a big green bud early in hibernation and I can document the gradual reddening of both bud and larva as spring approaches. So far it hasn’t quite been that perfect but there’s always next year - actually there’s only next year, being the final year of the series. But no doubt I’ll always pop to the woods to see what’s about even when not documenting the situation so thoroughly.

Just a quick mid month update as yesterday I was tempted back to the woods by the prospect of frozen ground and an enjoyable crispness underfoot (I’ve definitely had enough of wading through mud in the drizzle).

I didn’t conduct a full check but covered at least half with a good loop and recorded no losses. Jacob, pleasingly, is still with us.

Isabella had moved from leaf to bud and now seems tiny, so much so that I thought I’d try to contrast her with Jacob at the other end of the size scale.

The next full check will be at the start of Feb - as usual I’ll be holding my breath as I approach Jacob’s tree and start nervously scanning the twigs hoping to locate the one still ever so slightly bending under his impressive bulk.

Anna

Andrew

Agnes

[David M]

...Anyway - they do gradually change colour, and it’s a fascinating process that I’ve tried to document in previous years. They must be able to get some kind of colour read from the substrate they are in contact with, and as the head quite often takes on a different colour from the body, it seems most likely that this ability isn’t tied to their limited eyesight but is a feature of the larval skin. Although not very well studied i guess it’s probably quite common in caterpillars, and is no doubt the same kind of process that leads to the triggering of different colour morphs in pupae. I always see it most strikingly when rearing peacock (dark on the net cage, yelllow on the nettle stem) but of course many other species show similar variety...

Fascinating, Ben. Many thanks for highlighting this.

It'd be interesting to know the extent of range of skin colours that were possible; presumably only those exhibited naturally by their larval foodplants? For instance, could one turn a charcoal colour if the thin branch it opted to occupy had been slightly charred by an earlier scorching, or is that outside the scope of their evolutionary genetics?

[Benjamin]

Yes - it’s definitely a good question. Unsurprisingly they seem to be able to cope well with the usual shades of twig and the full range of buds, so greys through browns and greens through oranges/reds seem well covered. In terms of really dark individuals I’ve seen enough to think that this wouldn’t be a problem if a particularly dark twig were selected.

I put together some more extensive collages a few pages back….

I do wonder how they’d manage with anything more unusual though - perhaps spraying the twigs of some in captivity would produce results. They’re very fussy about where they settle down though, so I’d imagine it might be difficult to convince them to settle for something so daft. I suppose they could be forced, but I can’t see myself playing that game - I’m sure the losses would be significant and unacceptable for me.

[Wurzel]

More fascinating reading Ben It took me quite a while to find Agnes - for a moment there I thought you were playing a prank on us and making us stare at just a twig Looking forward to the Feb report - fingers crossed!

Have a goodun

Wurzel

[David M]

...I do wonder how they’d manage with anything more unusual though - perhaps spraying the twigs of some in captivity would produce results. They’re very fussy about where they settle down though, so I’d imagine it might be difficult to convince them to settle for something so daft. I suppose they could be forced, but I can’t see myself playing that game - I’m sure the losses would be significant and unacceptable for me.

Indeed, Ben. It'd be irresponsible to introduce such artificial factors just to satisfy one's curiosity. However, there must be occasions where trees have been naturally scorched during the summer by a minor fire. If, subsequently, females lay eggs low down on such trees, I wonder whether there's any scope for the larvae to adjust accordingly.

I'm sure, however, that fluorescent orange would be beyond them should the branches be painted thus.

[Benjamin]

With January finally behind us it was time for a full check to see how the 18 that survived December had fared in January.

4 losses were recorded. Thomas and Isabella were just 30cms apart and were always likely to either both make it, or be forever united by the digestive system of a jackpot hitting passerine. Unfortunately it seems it was the latter.

Also running out of luck were Anna and Jenny - neither of which (or neither witch) had made particularly convincing overwintering choices, and sadly I wasn’t too surprised to see their mournful silken pads now revealed and glinting in the sun.

But Jacob survives! He continues to transform himself into a beautiful green and orange bud (by far the biggest on the tree!) and despite being easily spottable from several metres out, he makes it into the second half of winter unscathed. I previously mentioned he looked like an offering to the tits, balanced as he is, all exposed and tipward of his horizontal twig. Having now read up a little more on his namesake who it seems pled guilty to the charge of witchcraft only to save his male lover(s) from death at the hands of the Spanish Inquisition, I worry that Jacob the caterpillar is showing similar self-sacrificing tendencies.

Couple this endearing quality with his apparently slim chance of survival and he’s instantly catapulted to the position of firm favourite (and if that doesn’t instantly seal his fate then he must surely be destined for greatness).

14/20 continue on into February….

Elsewhere elm flower buds are starting to swell invitingly - the flying saucers will soon begin to open….

[Wurzel]

Sorry to read about the four losses but that doesn't seem too bad a loss rate at the moment? I'm rooting for Jacob now -are you sure about his namesake - what with the changing colour and now the green and red isn't he the Jacob with the technicolour dream coat?

Have a goodun

Wurzel