Sunday, May 24, 2015

Final Instar

Iris larvae have now entered their final instar, in the wild in Wiltshire.  This is bang on time, and despite yet another poor May.  
Here's No 4, photographed today.  Incidentally, he's the only spring larva I've recorded on a narrow-leaved sallow - 



And here's an in situ photo of No 7, who has just changed skin (on May 23rd).  The cast skin is just visible, below his tail end - 



My other wild larvae have entered the 5th and final instar and wandered off up tree, which is rather inconsiderate of them, but normal.  Two are visible through binoculars.  They become increasingly mobile and sun loving in early summer.

At this stage it looks as though the Purple Emperor season will be on time, but the insect can get stuck for ages (4 weeks) in the pupal stage during poor Junes - and we may be due a poor June... .  Also, the two larvae shown here have ten days of feeding before they can start to pupate.

Watch this space...

Thursday, May 21, 2015

2nd instar overwintering

I've posted a couple of times about this before but as I got new confirmation of the phenomenon today I thought I'd post again.

The caterpillar I named Yudhiṣṭhira was tiny when I found him earlier this year and I suggested he was 2nd instar. Mark ('iriscientist') agreed. He shed his skin for the first time in 2015 between 9th and 11th May. He is now laid up again for a second moult, though still only about 12-13 mm long - a typical size for the 3rd to 4th instar moult. It is not possible that this is a 4th to 5th instar moult, at which stage the larva is typically 24-25 mm long.

Unfortunately, I have suffered a high loss of larvae over the last couple of weeks. The other two I believed might have hibernated in 2nd instar have both disappeared. A third, that I am unsure about, is still alive, but I haven't logged all her moults as she's a bit off the track and when I have little time I miss out a daily check. I will try and follow Yudhiṣṭhira through his next moults but there is absolutely no doubt now that he did hibernate in 2nd instar. The evidence I have gathered over the last few years suggests this is not at all uncommon in Switzerland.

Yudhiṣṭhira on 9th May, still laid up:


Yudhiṣṭhira on 11th May, newly 3rd instar:


Yudhiṣṭhira today, 21st May, laid up for his next moult:


About 200m away in the same woods is Agni, who moulted into 5th instar on 16th May:


He was still there when I checked today ...

Guy

Thursday, May 14, 2015

Hastening on ...

Agni, my top cat, is now laid up for transition into 5th instar:


He moulted into 4th instar ten days ago, on 4th May.

Most other cats are in early/mid 4th instar. This is Sarasvatī:



Baby Yudhiṣṭhira, newly 3rd instar, has changed leaves and is thriving and growing. He is now just over 1 cm long:


Guy

Monday, May 11, 2015

Close Encounters

Sue of "Countryside Tales" sends pictures of her close encounter with an Empress last summer.

May there be many more!












Shadows

Most of the cats I'm following are at head height or below - for obvious reasons. But one day recently I gazed into the higher branches of a sallow and spotted a cluster of nibbled leaves bearing the unmistakeable signature of iris. I then spent ten minutes craning my neck until eventually I spotted Nakula. Since then I have seen him most often by his shadow:


That picture is a heavy crop, taken with a super-zoom camera (x 42) at full extension.

Today he was again playing shadow games with me ... 


... but at one point we had an intimate encounter, when I think he suddenly became aware of my presence:


He didn't like it much and imediately turned around:


Elsewhere, and to follow up on a previous post, my smallest cat (Yudhiṣṭhira) moulted into 3rd instar yesterday. After his moult he was still under 1 cm long, as is obvious in this picture of him next to my baby finger:


Although perspective can distort size pictures, this one is not far off. My finger is touching the leaf and displacing it slightly to one side. This is a tiny cat and certainly not 4th instar. I think overwintering in 2nd instar is not uncommon in Switzerland. We have more protracted autumns than in the UK and recently I have been seeing purple emperors well into September - this male was photographed on 13th September last year (though not in my local woods):


Eggs laid late, or in the shadow of mountains (which can dramatically shorten the Swiss day) might not be able to reach 3rd instar by the time they are preparing for winter.

Guy

Monday, May 4, 2015

A question for the experts ...

I found Durgā in mid-September last year and so didn't witness any of her skin changes. On 28th April this year she appeared hunched up on her leaf, with yellowing shoulder pads, as if about to shed her skin. She remained in that state for the best part of a week, though I did see her moving her head during this time.

28th April:

Today she looks quite different and has moved to a new leaf:


But she is still only 10mm long, unlike Agni, who changed into 4th instar today and is over 15mm.

Is this natural size variation or is she perhaps one of the few larvae that hibernate in 2nd instar (I have definitely recorded this phenomenon before). Or, was that not a skin change at all, despite appearances? If she lives long enough I should be able to answer these questions over the course of the next couple of months, I suppose. Several other very small caterpillars have adopted a similar, hunched attitude, with the same shiny, yellow shoulders. Other caterpillars are significantly bigger.

Guy

The Old Me

In my local woods things are a little behind the UK, to judge by Matthew's last post. The first confirmed transition to 4th instar happened today and most cats are still small.

This is Agni, sitting on his leaf with his old skin at his tail. Is that another iris cat peeping round the leaf? No it is his old head, complete with horns ...



Guy