Benjamin

[jonhd]

X1, X3, etc. - puts me in mind of (Fireball) XL1 - how about cat names based on Gerry Anderson characters, next year?

Could even do a sponsored naming tombola!

BR, Jon

[David M]

Great report again, Benjamin. You sure are putting in some hard graft with these larvae.

It's always hard to know what's best when you are observing nature, but I'm glad you lent a helping hand to X1, even if it wasn't necessarily appreciated.

[Benjamin]

I must admit I’m not a big fan of the letter/number system Jon, but 20 is about my limit for themed names. Gerry Anderson characters would be excellent (if a little before my time) - I’ll bear it in mind!

Thanks again David - now spring has arrived every trip to the woods is a pleasure - the freezing drizzle has gone (just!) so the challenging part is over.

I’ve been very busy with other species, so yesterday (14th) was my first day dedicated to iris in about a week - doesn’t sound long but with several on the cusp of L4 a week ago, I was concerned that I’d struggle to relocate a few, at least.

As it turned out all 13 were present and correct - plenty of movement, but nothing further than a metre or two as the caterpillar crawls - essentially only movement to one of the adjacent sprays.

The developmental gap must be about 3 weeks at this point, with the most advanced (X1) now a week into L4 and looking just a few days off preparing for L5, while the least advanced (Mr Clean,X2) although greened, still look a little way off settling down for the L3/4 skin change. Here’s the updated list as it stands:

Lily L3 - pre moult
Billy The Kid L3 - pre moult
Mr Clean L3
Tiny Montgomery L4
Skinny Moo L3
Hollis Brown L4
Corrina L3 - pre moult
X1 L4
X2 L3
X4 L4
X5 L3
X10 L3 - pre moult
DD 1 L3

Although photography is often challenging on overcast days in woodland, i always take record shots of each individual, and have a bit more of a go at anything of particular interest. Yesterday the interest was all with Tiny Montgomery. I’m admittedly a little obsessed with the brilliance of caterpillar camouflage, and frequently frustrated with my inability to capture this brilliance in a photograph, but yesterday the stars aligned and i got the result i was after - in truth Tiny Montgomery made it so easy for me i could hardly go wrong.

The purpose of the iris horns has been much discussed, and although there could be an obscure function (some kind of ‘weather station’ as Matthew Oates suggests) I am entirely satisfied that their evolution and continued utility can be justified on camouflage grounds alone. I came to this conclusion watching L5 caterpillars disappear amongst sallow sprays last year, but it could hardly have been more obvious when watching Tiny Montgomery yesterday afternoon. I usually make a decent effort to select only the best from a batch of similar shots, but am going to indulge in some repetition here:

The obvious imitation of female catkins raises some questions. I looked at whether sallows of a certain sex were preferred last year, and came to the conclusion that both sexes were used pretty much equally. Certainly both are used, but I’m now not so sure that it’s equal. This year at least, when sallows are flowering profusely (perhaps due to drought conditions last summer?) it seems female trees have been heavily favoured. Of the 13 remaining caterpillars, 10 are on female trees, 2 on male trees and 1 on a tree too young to flower. I need to go back and check all the trees where larvae were found this year and last to get a better idea. It’s tempting to think that perhaps this year caterpillars on female trees hidden amongst catkins have simply survived better (as you’d expect), but nearly all the losses were pre catkin development, so this can’t be the explanation for my female bias. Of course this apparent advantage could be counterbalanced by an advantage that caterpillars enjoy on male trees, such as earlier leafing without so much of the resource being pumped into seed development. Who knows, but having two big horns clearly more suited to survival on female trees does seem like a pretty significant advantage for those that find themselves on female trees, and if egg laying females can detect the sex of the tree (can they?) then surely female trees would be heavily favoured (by which I obviously just mean that the increased survival rate of caterpillars on female trees will cause genes ‘for’ choosing female trees to spread throughout the gene pool).

Or perhaps location just trumps everything so that perfectly situated trees are always selected regardless of sex. This could well be the case, and with female trees being selected when all else is equal, could be the reason that we see a female bias (if we do) but not exclusive female selection.

A further confusing aspect of this is that eggs are generally laid low down (<4m height) and are therefore often below the flowering zone (flowers generally being more abundant higher up). Perhaps the conditions low down suit early instars (humidity, tender leaves etc) and the much documented habit of L4 caterpillars ascending the tree is as much to do with moving up into the flowering zone as it is to do with seeking sunshine (as is currently suspected). This L4 movement is actually not something I’ve encountered too much, and when they do move up it only seems to be about locating increasingly large leaves suitable for supporting their increasingly large bodies.

Hmmm - who knows, but it would seem that, at one time at least, the time spent amongst female catkins must have been significant enough to shape the caterpillar appearance.

A selection of others:

X1 - pack leader

Skinny Moo

X2 - held up on a very late leafing tree

X2 location - very few leaves

X4

[Pauline]

Another thought-provoking report Ben. It is so refreshing to read about such detailed study and research, especially when accompanied by excellent illustrative images. Thank you for sharing the results of your hard work.

[trevor]

Another great report Ben. Your images demonstrate how well the PE cats blend in
with their food source. Are you into predictions ? ie. when will they pupate, and
more importantly emerge as adults.
I know of two individuals who do this every year.!.

Wonderful work, keep well,
Trevor

[Wurzel]

Fantastic images Ben - they really do show the wonder of the mimicry, they disappear before your eyes particularly when they position their antennae in that way.

Have a goodun an stay safe

Wurzel

[Benjamin]

Thanks for your very kind comments Pauline, Trevor and Wurzel.

Trevor - yes - I wrote a post about predictions at the start of May and included a very early prediction based on the weather throughout May and June being fairly average.

“Currently i can imagine a season with an extended wait for the emergence to begin (nothing until July), promising numbers initially (as the field will have bunched up) but more of a ‘gentle fart’ than a ‘big bang’ in the second week of July and then the usual gradual decline with a few individuals flying late into August or even early September - at which point we can go searching for eggs again.”

Trying to be more accurate than that and naming the day of the first sighting is really just having a punt, but I am a gambling man, so I’ll go for July 2nd - probably at Knepp.

The accepted wisdom seems to be that a poor egg lay will lead to reduced winter predation and then potentially a good emergence if spring weather favours caterpillar development.

Much is made of the conditions around spring development of larvae with a potential big impact on numbers being envisaged. I’m not quite sure what is being imagined here as I only see spring conditions dictating speed of development, and nothing really impacting too much on numbers overall - but I’ve only just started looking closely, so may yet come across something of significance.

My approach has generally been to challenge the accepted wisdom, or rather keep an open mind with regards to it, and just report on what I see. So my predictions are based on what I observe at the sites that I monitor, and do not focus on emergence timings from previous years cross referenced with the emergence of other species (probably a more accurate way to make predictions overall and a method that any good record keeper can have success with, without ever setting foot inside an emperor wood!).

Of course the longer I keep in touch with my larvae, the better any predictions will be - I certainly hope to be able report on pupation timing and will of course keep my PD updated!

[millerd]

This all absolutely fascinating, Ben. How you manage to spot these larvae (even when you know where they are going to be) is astonishing. I don't think I could find an iris cat unless it fell out of a sallow onto my head (which they aren't known for doing). I shall continue to follow their progress with great interest.

Cheers,

Dave

[David M]

Thought-provoking observation regarding the 'horns' of the larvae and the female catkins, Ben. When put into the context of an image it seems extremely plausible.

Heartening that none of the cats have disappeared since your previous visit. Let's hope they can continue to avoid predation.

[Benjamin]

Thanks Dave, but I’m sure you’d have no trouble. Once you get your eye in they’re not so hard to pick out.

I’m doing ok so far David, but losing touch with the majority is inevitable - my job is to delay that point for as long as possible.....

May 19th.

Some photos and updates from a very enjoyable check up on the 13, well, unfortunately now the 12.

I seem to have been alone (or certainly in the minority) in thoroughly enjoying the spring weather of late - perhaps a little short on extended blocks of sunshine, but here on the Sussex coast at least, most days have been a mix of showers and sun. I suppose it makes it difficult to time a butterfly trip, but if you’re out in the field anyway you regularly experience the sudden heat of the sun appearing between parting clouds, and the associated buzz of activity that soon follows. The pervasive numbing effect of the cold drought of only a few weeks ago blown away by the much needed injection of warmth and water. The woods have responded and are now in their full spring glory. This has to be the best time to monitor iris - the long winter has been survived, and the remaining larvae can dare to dream of making it all the way.....

But, coming back to reality, not X10 unfortunately. It is quite possible, however, that this one has been forced to travel some way to locate leaves suitable for a newly attired L4 caterpillar. The effect of moth and sawfly larvae on the foliage is extensive now, with sallows only just coming into leaf hosting more individuals than they can comfortably cater for. This will only last another week or so, when the speed of leaf growth will overtake the capacity of the larvae to devour it, but for now it leaves an iris cat in the difficult scenario of struggling to find anything sufficiently large and undamaged to make a seat out of. I’m sure this is what caused X10 to disappear out of my searchable range - either that or he was picked off. I searched everything I could for well over an hour before reluctantly admitting defeat. I will return for another search, and to scan higher up branches on my next visit - for now he has to go down as AWOL but not quite ‘presumed dead’.

This will also happen to Skinny Moo as soon as she transitions to L4. She will find that her spray offers nothing to match her needs, and she will follow the path shown. I will lose her if she takes all but one of the options open to her when ascending the tree - the odds are not good.

Skinny Moo

her branch

her choice....

All the others pretty much look ok - I don’t expect to lose them just yet. X1 (the pace setter) has put on weight but not as rapidly as I expected, and remains a while off L5.

X1

Tiny Montgomery continues to show off all his survival skills - seemingly running through his entire repertoire while I settled in for some photography. He hasn’t learned the ‘tail-tuck’ (demonstrated by X4 below) yet though - something to work on.

Tiny Montgomery - the pick of his repertoire

X4 is in the doubly unusual position of being on a big old caprea style tree, and that tree also being male. No female catkins to offer protection for him, but he does have fantastically sized leaves that have quickly outgrown the moth/sawfly damage and offer him a multitude of potential residencies. As such, he has moved very little, and is perfectly happy on his local spray. He has mastered the ‘tail-tuck’, but missed the lesson on shadows - a big error on such large, undamaged (relatively) leaves perhaps. We’ll see.

Excellent tail-tuck

Could do better

Corrina will not thank me for this photograph. Still with one foot in winter she’s covered in detritus and having all the imperfections wrought by a long cold winter highlighted by some uncompromising backlight.

Corrina

Billy The Kid is another to recently discard his damaged winter wardrobe. I carefully repositioned his spray for a record shot and upon releasing him back to his correct position he began eating his morning meal. This gave me the opportunity for a few more shots, and also to waste some time trying to line him up with a gap in the canopy behind. The result was predictably gimmicky and reminded me why I should refrain from such time wasting in the future!

Billy The Kid

Breakfast

Hmmm

Lily L3 - pre moult
Billy The Kid L4 - early
Mr Clean L3 - pre moult
Tiny Montgomery L4 - mid
Skinny Moo L3 - pre moult
Hollis Brown L4 - mid
Corrina L3 - pre moult
X1 L4 - late
X2 L3 - pre moult
X4 L4 - mid
X5 L3 - pre moult
X10 AWOL
DD 1 L3 - pre moult

[bugboy]

Love that last shot where you've managed to highlight the cat in a halo of blue

[David M]

The ability for these larvae to hide in plain sight is astonishing. In just about every image, I have to maximise the shot just to be able to locate them!! Not only are they superbly camouflaged by way of colour and pattern, but also by posture, exemplified perfectly by Tiny Montgomery in your fifth image, Ben.

Looking forward to the next sequence.

[Benjamin]

I appreciate your comments as always guys.

Just a quick check up on the remaining cats today. It hailed, I got soaked, my fingers went numb and as I trudged around the mud with my ladder I wondered, once again, why I haven’t owned a coat for a decade.

Mr Clean and Hollis Brown were MIA. I’m more hopeful that Hollis Brown will be relocated in better weather. Mr Clean, I fear, was snaffled in his pre moult torpor.

All the other pre moult L3s from my last visit are now L4, which means we narrowly missed out on breaking Matthew Oates’ remarkable record from 2010 when he was still in touch with a wild L3 on the 25th of May. I can’t imagine how things could have been much slower than this year. If we can’t beat it after record breaking cold in April, followed by a record breaking wet May, then we never will - in Sussex at least. In the northern woods I imagine there are still L3s.

But maybe I’m just getting caught out by the headline writers again. It was cold and dry in April, and it has been a bit wet in May, but if I hadn’t been told it was all so astonishingly unusual I’d have just put it down to good old British spring weather.

Anyway - we didn’t beat the record. They’re all now L4, with X5 only just joining the club today, and X1 preparing for L5 at the other end of the spectrum.

X5 couldn’t hang on for the record

X1 preparing for L5

With some fine warm weather on the cards it is likely that these L4s will develop quickly and transition to the L5 end game at the start of June. How fast the L5s hurtle towards pupation will of course depend on the weather - I only hope I can keep in touch with a few.....

X4

X2

Billy The Kid demonstrating the dangers of communal living. Damage from moth larvae is extensive in his neighbourhood.

Corrina

Tiny Montgomery

[David M]

Thanks for the update, Ben. Shame a few are MIA but as you say, trying again in better weather (hard to think how it could get any worse) might pay dividends.

Given that we now seem to have a warmer, sunnier period in situ, one suspects that these cats will make up a little lost time. Hopefully we'll avoid the situation in 2020 when conditions were exceptionally good until early June and then collapsed with a couple of weeks of truly awful weather during the pupation phase.

Fingers crossed.

[Benjamin]

They will certainly speed up now David, and yes, a smooth run with sensible weather would certainly be best for development - although to be honest, they seem pretty well capable of dealing with whatever comes their way. Anything too challenging and they just delay development and wait it out.

Quite a week in the woods:

Lily L4 MIA
Billy The Kid L4 MIA
Mr Clean L4 MIA
Tiny Montgomery L4 late
Skinny Moo L4 early
Hollis Brown L4 MIA
Corrina L4 MIA
X1 L5 early (assumed)
X2 L4 early
X4 L4 - late
X5 L4 MIA
X10 L4 MIA
DD 1 L4 early

The majority of those MIA are relatively young L4 larvae and have relocated as a result of competition with moth larvae - primarily Winter Moth and Mottled Umber, but also others and various sawfly species.

This is always a problem, but has been exacerbated this year due the the delayed leafing of the sallows, leading to a mass of hungry mouths competing for every leaf that begins to grow. The severity of the damage depends on the relationship between leafing time, and hatching time of all these species, with late leafing trees apparently unable to out-leaf the demand. Early leafing trees are able to put on enough growth before attack to comfortably cope with the onslaught when it arrives.

X5 forced out. See also Billy The Kid photo from last post

Anyway - the frustrating result of all this from our point of view, is that any iris cat caught up in all this will soon find himself unable to remain in his neighbourhood. He is forced out to search for food, and undamaged resting leaves big enough to support his weight and offer him the protection he needs. In my experience, this is not a move that iris caterpillars ‘want’ to take. If ample feeding and resting opportunities are to be found in their original neighbourhoods then they don’t tend to move. Perhaps they may seek a sunnier location, if they are in shade and the weather is cool, but I have observed larvae in heavy shade but otherwise perfect conditions stay put and pupate very close to their hibernation spot. This is all fairly obvious - there has to be a very good reason for a bright green caterpillar to walk for several metres along brown branches that are regularly monitored by birds. Seeking the warmth of the sun could be one if development is very slow, but finding food and something to rest upon in relative safety is certainly a good enough reason when those things are no longer available on the doorstep.

There is also the journey to pupation to consider - very often caterpillars seek better pupation sites higher up the tree, so if this journey has to be taken at some point, then it could be of benefit to take it sooner rather than later, and thereby also benefit from the improved conditions (be they warmth, leaf quality etc) for the remainder of the growth phase.

Of course we can’t know the exact motivation, but in terms of tracking them to pupation, this move is critical. Relocate them after this and the odds of following them all the way improve dramatically.

Skinny Moo also relocated as predicted, but thankfully chose the path that kept her within reach. We are encouraged by Matthew to honour Denys Watkins-Pitchford (‘BB’) and keep alive the tradition of calling ‘Ai! Ai!’ when we discover a caterpillar - that isn’t really me but then neither is the double ‘fuck yeah’ that burst forth when Skinny Moo was relocated - if any dog walker turned and caught sight of me up my ladder at that moment they would have rightly quickened their pace. Blame the preceding several hours of bitter disappointment (loss after loss) and the never ceasing onslaught of American culture. Her situation is such that she may move again as she grows, but hopefully this spot will be suitable for this instar at least....

Skinny Moo

X2 is a beautiful caterpillar but at a height almost impossible to photograph unfortunately. A young L4 with extensive black markings on the underside of her horns that continue right down to her mouth. I think this is a variable characteristic of younger instars (certainly 3 & 4) but doesn’t get mentioned very often - by L5 the black has disappeared. It is probably the most striking difference between L4 and L5, but as the majority of photographs are of head-down (having been thoroughly disturbed) larvae, it is rarely picked up. Of course anyone looking closely or captive rearing will know this difference well.

X2

X2

X2

Interestingly a tree that has received eggs for the last 3 years, is only just coming into leaf. The egg I found there this year was predated, but had the larva hatched and survived the winter I’d have been interested to see if it could have coped with such a late start. It would only just be getting going now, in late May!

Late sallow

Matthew’s record in his book for the latest he’s seen a wild L4 is May 30th, but he informs me it is actually June 2nd. Either way, several of my L4s will beat that this year - if only I can keep track of them to prove it.

DD1 reducing shadow

So a much reduced field, but a few remaining that, if they survive, could stay local enough to give me a chance at finding a pupa. It’s looking less likely this year, but we’re still in the game for now.

Tiny Montgomery still waiting for L5

X1 22 days as L4

[trevor]

Exciting times ahead Ben!. Let's hope the Emperor shows well this year.
Last year was not the best, the weather played havoc and I always seemed
to be in the wrong place at the right time!.

Still all good fun!, Stay safe.
Trevor.

[Benjamin]

Indeed Trevor - even in a poor year you can get lucky - fingers crossed!

Just squeezed in a visit to confirm that both X1 and Tiny Montgomery are now L5 - both yesterday (29th) I assume.

Tiny Montgomery lining up nicely

X1 working out his L5 neighbourhood (I hope)

[Padfield]

Interesting question, what is the latest date for a cat still to be in L4. I've had a quick look through my piccies but as I have several thousand of iris cats, and it's not always obvious which instar they are from a picture without scale, I didn't come to a conclusion. I think I've had 4th instar into the beginning of June, from a cat that overwintered in 2nd instar, but I couldn't remember his name immediately to search for him.

These photos of Ganeṣa were taken on 28th May, 2015. He was right at the top of a sallow, peering off a leaf, so I couldn't get closer, but the two heads are a bit of a giveaway - he must be in the middle of the transition from 4th to 5th. Gave me quite a scare when I first spotted him ...





Guy

[Wurzel]

That last shot Ben is an absolute corker! It brought a smile to my face and made my younger daughter chuckle all the way up stairs She said it looks like a ghost although I reckon it has more of a surprised look on its face

Have a goodun and stay safe

Wurzel

[David M]

...Quite a week in the woods...

Quite a week indeed, Ben. Looks like they're getting their skates on, which is hardly surprising given they have finally experienced some proper, summer weather!

I'm loving these context shots, as well as the images of the larvae themselves.

My money's on Tiny Montgomery