Benjamin

[Benjamin]

Thought I’d interrupt my scintillating commentary on caterpillar losses to post here something I put up on the Sussex BC page:

“Just a request for people to report any marked (topside elongated black mark, underside colourful dot) small tortoiseshells that they might encounter. I’ve been having another look at parasitoids in the nettle feeders and have ended up with hundreds of STs to release. I don’t really have any great expectation of seeing any of them again (marking them was a bit of an afterthought really), but I (and my helpers - good at releasing not so good at rearing!) would be very interested in location if anyone happens to spot one over the summer, or next spring. They are being released at various coastal sites from where they were collected, and this generation will probably gradually head north (I guess). I will also be releasing similar numbers of the next brood later in the summer. Thanks!”

By the way my marking skills improved dramatically over the course of the 300 or so attempts - some of these were the early attempts and are far from my best (honest!).

Also I decided red dots were probably a bit too conspicuous for something that may overwinter, so I moved on to more subtle colours after that.

As I say - bit of a long shot that anyone will ever spot one, but seemed worth a go given that I had so many to release anyway (Neil will disagree - he assures me he still needs more photos of small tortoiseshells and will never forgive me for graffitiing so many of these gorgeous Sussex rarities! I have promised him a pure batch by way of redemption).

[Benjamin]

Will get back to the iris cats soon - now the ST collecting, rearing, marking, releasing marathon is coming to an end. Peacocks are ready for collection though

[trevor]

I have noticed that ( at the moment ) stinging nettle growth is lush.
Lets hope this will assist in boosting the Small Tort population.
At this stage in the season I have still only seen one in East Sussex so far.

Keep up the great work!.
Trevor.

[David M]

...I’ve been having another look at parasitoids in the nettle feeders and have ended up with hundreds of STs to release...

You sure are ultra-busy right now, Ben. Given how scarce Small Tortoiseshells generally are round that way, one would hope they'd stick around rather than 'head north'.

Your post is a reminder for me to look out for summer brood Torties now. They should be about any time soon.

[Benjamin]

Yes Trevor - stinging nettles are booming right now, when I guess they might have started to struggle in a particularly hot/dry year. They did, however, struggle badly throughout the dry April, with growth stunted and leaves curled to retain moisture for several weeks. A few wet weeks later and they’ve never looked so good. Peacocks will benefit, but then they always seem to do well.

STs are now emerging in good numbers (from my cages but from what I have seen, also in the wild). In several days searching Sussex sites I found surprisingly good numbers of ST nests. They were pretty much everywhere I’d expect them to be, and in really good spots up to 10 webs would be clustered in a 20 or so meter stretch. I’m new to Sussex but this search was a very similar experience to searching for webs in the midlands 20/30 years ago - something I probably used to spend too much time doing if I’m honest.

So we don’t see many STs in Sussex, but it isn’t because they don’t breed reasonably well here in spring - or at least, so it appears after an initial (limited) investigation.

Yes David, it would be nice if they stayed local but perhaps that’s a significant part of the problem down here. I’m not sure if we really know how migratory they are, and with the first brood emerging ever earlier, perhaps the tendency in this brood to head north is being increasingly triggered. Just thinking out loud, but if they do stay local and breed straight away, then I would expect to find plenty of nests popping up over the next month - I will be searching.

[Benjamin]

Back to the serious stuff :

Guy - I think Matthew Oates had June 2nd as his latest ever L4, but he has just this year recorded one on the 5th so that’s the new record as far as I know. I had several that must’ve changed to L5 between the 3rd and the 5th but unfortunately I wasn’t around to confirm date, and when I did return most had relocated never to be found again.

Glad the cat pictures are entertaining your family Wurzel - but I think the one that tickled you and your daughter was Guy’s - it is a great shot though!

Update from the woods 8/9th June:

I’ve now had time to have a really thorough search for all those that have recently been lost but unfortunately I’ve been largely unsuccessful and am down to the final 3.

X1 L5 late
X2 L5 mid
Skinny Moo L5 mid

I’m very surprised X1 has stayed put for as long as he has (I’m not sure about sex but can’t be bothered to keep writing he/she his/her and I certainly don’t want to go down the gender neutral rabbit hole - I can’t imagine it’s very iris. I suppose they/their works but I’m not too keen on that - I’ll just assign a sex and deal with the repercussions when they come….I’ll probably have to apologise to the cats or something), as his spray is only just catering for his needs (look how he makes even a small leaf work!) and access to the higher branches is relatively easy. He will go, any day now……

X1

How I’ll lose him

X2, the beautiful ‘badger-faced’ L4 is now mid L5 and has lost those lovely L4 markings. She (because she’s pretty - oh dear - more trouble…..) seems relatively content on her spray and although she could quite easily find her way up higher, there’s definitely an outside chance that she might pupate where she is. Still most likely 10-14 days of L5 still to go though, so plenty of time to lose her.

X2

X2

The final one, and the last of the Dylan theme is Skinny Moo. She’s relocated a couple of times now, but thankfully quite predictably and I’ve been able to relocate her each time she has ascended to higher sprays. Another one with at least 10 days of L5 still to go, and with easy access to a mass of out of reach sprays, it seems very unlikely that I’ll keep in touch with her for much longer.

Skinny Moo

Skinny Moo

Elsewhere in the woods (I thought I should add some occasional colour) several species of dragonfly have started to dominate the airspace (until early July anyway!) - this broad-bodied chaser posed nicely as they always do, a red admiral kept returning to his favourite stump to perform his latest vanishing trick, and one of my favourite moths, the buff-tip, freshly emerged.

And finally - remember old Bobby Fischer who sacrificed himself for the sake of his art? He continues to wither and retreat - pretty soon all that will be left will be the ‘V’ of his horns. Wow - rock star.

Although having said that, a sad face does seem to have appeared looking out at the world on the back of his head. Perhaps he does wish he’d gone the conventional route, and would soon be dancing through the treetops in midsummer, drunk on sap and high on pheromones? Gosh - heavy stuff.

[Pauline]

Your little helpers have an excellent role model Ben. I sincerely hope that you do not lose track of all of the remaining 3. If that happens I think I shall be more disappointed than you! Fingers crossed for the next installment.

[Wurzel]

Great work with the Small Torts Ben and good to see you roped in some assistants I checked back on the cat post - your final shot is still a cracker but that's the problem with a wireless mouse, the slightest nudge and you're on another page Keep up the great work!

Have a goodun and stay safe

Wurel

[Benjamin]

Thanks for the encouragement Pauline and Wurzel - kind words much appreciated.

Yesterday I took Skinny Moo into captivity as a Tachinid egg had appeared glued into one of the folds of her skin. It’s a shame to interfere, especially as I have so few remaining under observation, but I wanted to check again that iris cats are able to defeat this particular parasitoid.

As documented at the start of this diary, Deontay survived such an attack last year without any negative impact. My conclusion was that his internal defences (encapsulation response) destroyed the Tachinid grub suggesting that particular parasitoid must have been a generalist that enjoyed greater success with other species.

To have it happen again so soon, however, and in such a small sample, does suggest that it could be a very common occurrence. It would seem odd, even for a generalist, to continue to attack a species that only ever represents a waste of eggs. Perhaps that’s perfectly reasonable as long as the generalist’s instruction to ‘lay on any big green larvae’ results in more successes than failures, but I would have thought as distinctive a caterpillar as iris that represented nothing but a waste of resource would gradually become avoided.

But I suppose I don’t know anything about this particular Tachinid - for all I know, and for whatever reason, it may have only relatively recently encountered iris.

Clearly I’m just guessing, but I couldn’t resist another opportunity to potentially learn something about this relationship, so Skinny Moo is now in my garden.

Skinny Moo with Tachinid egg

Tachinid egg close up

In other news - the last few 1st brood small tortoiseshells have been marked and released. The parasitoids have been unexpected and interesting but I’ll write that up when I’ve finished getting them all identified.

[Katrina]

A quartet of beautiful Small Tortoiseshells .

[David M]

Fascinating insight into the tachinid parasite, Ben. I too hope Skinny Moo will be alright. You've done the right thing.

Love the Tortoiseshell quartet. I reckon seeing four of those in certain parts of the south east is more like an annual total rather than a simultaneous one!!

[Benjamin]

Thanks Katrina and David - they may be captive reared and somewhat spoiled by my pen, but they are still stunningly beautiful and a pleasure to be around. I released a batch at a local nettle patch and for once they hung around - watching chases of 6 or 7 males takes me back to some of the very best ST years of my youth. I had forgotten how aggressive the males could be - ridding the airspace of anything that dared enter - more than one emperor dragonfly driven off at top speed over the neighbouring hedge. Had a purple emperor entered the arena I’m not sure where my money would have been (don’t tell Matthew or Neil I said that!). I am a big fan of small tortoiseshells.

The iris caterpillar season is now officially over - for me anyway. I have no larvae left under observation in the woods, but having struggled hard to keep track of L4/5s I’ve had some considerable luck at the end with the final two cats being wonderfully unadventurous by pupating very close to their final feeding positions!

X1

X2

X1 pupated on the 12th, and X2 on the 16th. Remarkably close considering that for most of the spring these two have represented the two ends of the developmental spectrum. X1 for example, became L4 on May 7th, whereas X2 had to wait until the 24th. A week or two of serious June heat really sped up the back markers, and with X2 being a noticeably smaller pupa than X1, it does seem like they were rushed through.

X2 unusual markings in L4

X2 under leaf

X2 location

They are both male, and depending on weather, should emerge (if they survive!) right at the end of June or during the 1st week of July. Skinny Moo (in captivity with Tachinid egg) is female and pupated today (18th). This all looks good for the 2nd week in July being the best time to be out looking for iris, although my punt on the 2nd of July being the date of the 1st sighting does now look a little late.

Also the very last of the STs are now emerging. Peacocks pupating soon.

Last of the STs

[Benjamin]

Earlier this year Mark Youles first showed us that although Apaturinae larvae do not fluoresce under UV light, the iris pupa certainly does.

I have been waiting for this period to test this for myself, and to see how useful it could be in terms of my field work.

In short - it works, and it’s very useful!

Walking around lonely woodland in the middle of nowhere at night is not really my cup of tea I must confess, but I had to check my study site to see what I might have been missing. Although finding loads of new pupae might have been fantastic on one hand, I am relieved to report that I found nothing I hadn’t already identified. The two pupae I have under observation, that have been tracked as cats since last autumn, lit up like beacons, but nothing else was discovered.

I had already come to the view (by searching high up for the silked-on leaves created by pre hibernation L3s) that the out of reach part of the sallows are not full of iris cats as I once worried, and that in fact searching thoroughly for silked-on leaves in autumn is a sufficiently good method to locate pretty much everything within a study zone. Using a powerful UV torch to search everything including the high up areas of mature trees I have been able to confirm this view.

I am much more confident now, that the 50 or so caterpillars I find in hibernation every year at my main site, are very likely the bulk of the overwintering population. I would expect this number to be much higher after a good egg lay - so far I think I’ve experienced two really quite poor years. Of course there are blocks of woodland not too far away that will provide more adults during the flight period, but in terms of the 1km2 (or so) epicentre of this population, I think I track them down with a high success rate.

But - I still can’t be sure - an excellent flight period with more adults than I’m expecting will send me back to the drawing board.

X2

[millerd]

Absolutely riveting stuff, Ben. Following the iris cats has been a real adventure! I'm also a fan of Small Tortoiseshells, and have raised hundreds over the years since I was a kid in the sixties. Your account was most evocative: memories consist largely of the contrast of the pain resulting from the gathering of huge amounts of fresh nettles for ravenous last instar caterpillars compared to the joy of releasing dozens of beautiful insects on several consecutive early summer mornings. All my children took a great interest in the latter part, but strangely not the former... It's great seeing yours getting involved!

Cheers,

Dave

[Benjamin]

So why do iris pupae fluoresce?

I have a theory that this is a mate location strategy. It would seem very strange that something so brilliantly camouflaged for its entire life suddenly, with the final skin shed, becomes lit up like a beacon!

As usual I’m just thinking out loud about topics I don’t really understand at all, but there is bound to be a survival cost to fluorescence - most likely increased predation by birds or rodents that can see UV, so there must be a benefit significant enough to outweigh this cost, or else fluorescence would have gradually been selected against. That is unless it is an unavoidable unintended consequence of sallow and iris chemistry - but that seems far fetched given that many sallow feeding lepidopterans don’t fluoresce, and nor indeed, does the iris larva. 

I’m not imagining the pupae are lit up to predators in the same way as they are under the beam of my torch of course, the small amount of moonlight might be sufficient for a slight glow, but concealed as they are on the underside of leaves, this may not give their position away in any significant way. But in the day, with sunlight catching them at the right angle they may really light up amongst the dark foliage.

The compound butterfly eye is probably able to see UV as well as anything else (Is it? Just making it up as I go along now - certainly plenty of butterfly behaviour appears to depend upon UV appreciation), so when we see early season males relentlessly searching the sallows it could be that it’s pupae that they’re looking for.

There is some suggestion, from captive breeding accounts, that females need to be at least a couple of days old in order to become sexually mature and receptive. Although I have no experience of this myself, it seems reasonable that a big powerful insect like this might require this kind of time, and so it seems unlikely that sallow searching males are looking for freshly emerged females, and more likely that they could be establishing whether an area has pupae, before later setting up a territory in the vicinity.

That’s not to say that they won’t interact with a female if they happen to come across one, just that the purpose of this well known morning behaviour, might be slightly different to that which is currently imagined.

This appeals to me as a theory because I see iris as an insect living at potentially very low densities in vast European forests. I realise the current thinking is moving away from this view, but I’m still there. I see a powerful flyer covering great distances to locate the next hole in the canopy where enough light can penetrate to allow young sallows to grow. Whether these areas of regrowth are caused by topographic features, tree fall, animal behaviours, or some other means, they could be few and far between and must be located and then searched. If males find pupae, then they set up territories nearby, and if females find sallows they lay before heading off across dense canopy to the next potential site.

That’s not to say iris isn’t adaptable. This ability to travel distance and locate suitable habitat, as well as other individuals (as pupae or adults) makes it well suited to our fragmented landscape. Knepp, for example, could be viewed as a giant ‘hole in the canopy’ (with, at least initially, a huge amount of young sallow growth) but instead of a forest canopy we now have the surrounding mix of inhospitable farm land and urban sprawl. Knepp represents an oasis in the desert, and one that iris is perfectly suited to find and exploit.

Anyway - please tell me if there is another reason why they fluoresce - I’m very open to the idea that I’m missing the blindingly obvious, or completely misinterpreting how fluorescence might work in reality!

[Benjamin]

Cheers Dave - didn’t mean to ignore you in between those long posts! Glad you and your kids have had similar experiences - hopefully the next generation won’t lower their standards to the point of accepting, as standard, painted ladies in pots of artificial gunk! I can’t imagine the memories will be as lasting, but then we do romanticise the past.

[Katrina]

Wow, a bunch of ST pupae and fluorescent PE pupae fascinating postings again.
I am impressed with your dedication and posts.

[bugboy]

Some fascinating posts here (and I shall be keeping a keen eye out for any unusually marked Tortoiseshells during my forays into Sussex this summer ). I was interested to read your theories about why the pupae fluoresce. We should keep in mind that how we see this ability is of a completely artificially manufactured way. I would imagine how animals with the ability to see into the UV wavelength naturally see it very differently and maybe insects brains process the information in a completely different manner than to say bird, leading to very different world views. Like you say there must be an evolutionary advantage to it. Maybe if we factor in the way leaves reflect and scatter light the florescence makes them invisible rather than like glowing beacons. Like you I'm thinking out loud as I write and have no real facts to base my thoughts on.

On another subject you postulated in an earlier post, the use of the horns as a means of camouflage against female Sallow catkins. Perhaps they don't need to be on the female trees for this to be a viable strategy. A few weeks ago at Strumpshaw Fen, on a cloudy day, I took to looking for Swallowtail pupae in and around clumps of Milk Parsley (trust me this is relevant). Predictable I found none but whilst looking I was struck by how some of the sedge flowers bore a remarkable resemblance to plump Swallowtail larvae, especially at a quick glance (my last post on page 155 on my PD). That got me thinking that given the birds that will the their main predators in the summer are currently the same birds frantically searching for food to feed hungry nestlings, by the time the caterpillars are big fat green and black things the birds have already learned to ignore anything that looks like them, they don't need to be around at the same time. It may even work better since they are now less likely to investigate them, already assuming they are inedible. The same thing may work with iris cats. The hungry Tits searching through Sallow thickets quickly learn to pass over anything that looks like a catkin, the camouflage therefore working no matter what sex sallow the cat happens to be on. Just me thinking out loud again

[Wurzel]

Some really interesting reading there Ben. One bit made me trawl through my memory and that was this bit:
"There is some suggestion, from captive breeding accounts, that females need to be at least a couple of days old in order to become sexually mature and receptive." I recall reading about some tropic species for which this isn't the case and they commit 'pupal rape', literally tearing at the the pupal case the mate with the female inside

Have a goodun and stay safe

Wurzel

[Pauline]

This has to be one of my favourite diaries. I am so enjoying reading about your discoveries, your thoughts and theories. Have you any plans to pull all of this together in some shape or form so it can be read in its entirety and/or used to refer back to at some point in the future?