White-letter hairstreak advice please

[Padfield]

As I passed one of the elms in my local meadow today, I noticed a small branch broken and dangling - a direct or indirect consequence of the storms, which brought down a neighbouring poplar, destroying a sallow and tangling with this elm. In case it should have white-letter hairstreak eggs on, I detached it and examined it. I quickly spotted a hatched egg and took the spray home with me.





Somewhere in these unfurling flowers is a caterpillar - or more than one - I hope:



I couldn't find it, but I didn't want to probe and risk disturbing it.

I have put the spray in a vase of water, as if it were cut flowers. Will the flowers open? How long in a vase of water will the spray continue to feel 'living' to the caterpillar(s)? If I find a caterpillar, should I immediately try to transfer it to a living part of the tree or is it safer to let it grow up a little on the broken spray?

If anyone has any advice I would be grateful. I've successfully transferred unhatched eggs back to elm trees but never hatched ones.

Thanks in advance!

Guy

[Pete Eeles]

Hi Guy,

"Will the flowers open?"
Yes, to some degree.

"How long in a vase of water will the spray continue to feel 'living' to the caterpillar(s)?"
A couple of weeks. Enough for them to feed up, moult, and emerge outside of the bud. Of course, the challenge here is the accelerated development if kept indoors (or even in a walled garden), so it might be worth transferring them back to a living plant in the wild at some point.

The challenge is, of course, finding the blighters, because they are tiny. I've kept them in a cool place (indoors) with the spray in a jar, and with the jar over a white sheet of paper. It's then easier to locate the larvae based on the frass below the larva.

Cheers,

- Pete

[Padfield]

Thanks Pete, that's very helpful. At the moment the vase is outside in the porch. I might bring it in and put it in the spare room, with white paper beneath as you suggest. Everything will happen faster inside, but if it helps me find the caterpillar more quickly too it will help me return it to the wild sooner.

Guy

[Matsukaze]

This insect is a master of disguise and each stage is harder to find than all its other stages. When rearing them, it is easier to work out where they are by looking for their frass and feeding signs rather than trying to spot the larvae themselves. In the wild, most feeding damage seems to get caused by moth larvae, which I can't help suspect that the WLH is impersonating...

[Padfield]

This insect is a master of disguise and each stage is harder to find than all its other stages. When rearing them, it is easier to work out where they are by looking for their frass and feeding signs rather than trying to spot the larvae themselves. In the wild, most feeding damage seems to get caused by moth larvae, which I can't help suspect that the WLH is impersonating...

You're right, Matsukaze - it is a real master of disguise. That said, it is one of the few species of which I've photographed all stages in the wild and I seem to be quite lucky with it. I've not seen all instars though. The first and second instars have thus far eluded me, at least partly because in Switzerland they happen in the Easter holidays (when I'm usually away) but also, doubtless, because they are just so difficult to see. And on top of this, in winter the elm branches spring up above head height and they stay there until the summer leaves weigh them down again.

I set up the spray inside today, with white paper beneath, and hope some frass will become visible over the next few days.

Guy

[KeithS]

I find woody cuttings such as elm last much better in water if you peel off a few inches of bark at the bottom where you stand it in water, to expose the soft stem inside. It helps with the water take up. A scissor blade is a good scraper.

Apologies if you do that already...

[Tony Moore]

Pete's trick with the frass is spot on. You will see frass before larva. Forgive the basic stuff, but do not try to move the larva yourself as it is difficult to tell if they are about to moult - they will find fresh food themselves if it is in the vicinity. If possible move the twig outside or somewhere cool or you will have a very early imago . If the twig is not caged, you will have the devil's own job finding the pupa...

A freshly eclosed WLH is truly one of nature's miracles.

Tony M.

[Padfield]

Thank you Keith and Tony - and my apologies for not updating this thread for so long. I am a complete novice at keeping caterpillars (I never collect from the wild except to save tiny lives) and never mind being given advice.

The upshot is that there was no frass. The only things that fell from the flowers were anthers. I observed for two weeks, while the flowers died, and examined the white paper beneath every day.

I found a hatched egg on a healthy branch a week before I found this one, so it is reasonable to hope the present caterpillar had already matured enough to have left the broken branch of its own accord before I fully detached it. The speed with which the flowers died, despite my following your advice, suggests it had already been broken a day or two before I spotted it.

Leaves are now beginning to unfurl. I should soon be able to start looking for caterpillars on the living trees.

Guy