Wednesday, November 18, 2020

Into Hibernation, via Dangle Leaf

Yet again, the weather's been ridiculously mild in early November, when Purple Emperor larvae were seeking to enter hibernation (or diapause, if you like). Some were crawling around for two or three hours, on different days, often ending up close to where they started. It remains to be seen whether they've wasted valuable energy reserves doing this.

To date, I have found 12 in hibernation, at two different sites. Interestingly, the five in Savernake went into hibernation a week earlier than the seven at Lambourn. Twelve is a reasonable sample size for monitoring winter survival, especially after a poor egg lay season.

I've named them after some of the politicians we all love so much (many of them will get predated by tits). Here's 'Donald', who spent more than two hours crawling around on Nov 9th, and moved again on the following day:-

He eventually conked out, curled around the underside of this thick branch, in a most unphotogenic pose.  

Most of the twelve are, as usual, aligned on narrow stems next to buds, like 'Nigel' here - 

But two are on well silked-on leaves - 'Boris' and 'Ivanka'. These are the first I've recorded hibernating on leaves in the wild (though Ben Greenaway had three do so last winter in Sussex, one of which survived). Here's Ivanka -

Note that she changed position by 180 degrees between Nov 2nd and Nov 16th.

Here's 'Boris', but he's difficult to photograph - 

And here's one of the loveliest 'pillars I've ever seen, the adorable 'Priti' - an unusual golden colour form conked out on the upperside of an old branch (+ lichens, moss & Veiled Liverwort). I don't think she'll stay there, as it's a very sunny position - 

Three of these larvae, including the adorable 'Priti', were found by Dangle Leaf - a technique for finding hibernating iris larvae by looking for vacated silked-on feeding leaves at leaf fall time, and then tracking where the 'pillar went. Ordinary leaves just fall off, but some of those that have been used by iris larvae remain attached, tied on by silk: the petiole itself breaks, as normal, but the leaf is then held on by the silk, and spins distinctively in the breeze. Here's what to look for -

I recently discovered iris in my local wood via Dangle Leaf. Ben has some success with it in Sussex, but it seems to work better with his Grey Willow hybrids than with my Goat Willow-type trees. There's an excellent German youtube piece explaining it:

Good luck with Dangle Leaf, in sheltered places. This has been a very windy autumn and the Dangle Leaf Season may be short...

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