The Remarkable Black Hairstreak 30th May 2019

The commencement of  June finds me anticipating the imminent flight season of Black Hairstreaks, one of Britain's rarest and more secretive butterflies and to be found only in fifty or so colonies in the East Midlands, an area which includes my county of Oxfordshire and the neighbouring county of Buckinghamshire.

Black Hairstreak nectaring on Wild Privet

Fortunately I know of a Black Hairstreak hotspot where last year, which was by common consent a very good year for this butterfly, I was fortunate enough to see over forty in one small area of Blackthorn, their favoured larval food plant and on the leaves of which the chrysalis  is placed.

This year I determined to return to this same hotspot and see if I could find some of the chrysalises, reasoning that as there had been so many butterflies last year, consequently there would have been many eggs laid. These eggs would have lain dormant through the winter and then given rise to a reasonable number of caterpillars that would have hatched in Spring this year and now pupated, ready to emerge as a butterfly in June.

I wound my way along quiet country lanes that passed through lush meadows until I came to the spot I remembered and, as it was last year, so today it had become a glorious sunny afternoon as I took the sheltered and sunlit narrow track that winds its mysterious way through thick blackthorn stands, crowding in on the track from either side.This is prime habitat for Black Hairstreaks, although today my search was for something even more elusive than the butterfly itself.

I had set myself a stiff task but one at which I was determined to succeed. It might take a while as I had the place to myself with no possible help from other enthusiasts but that is how I prefer it and there was no hurry. Time was for once my ally and in fact it was a delightful pleasure just to be here in this sheltered and peaceful place.

Stands of Blackthorn

A Black Hairstreak chrysalis is an absolute wonder of disguise. It is tiny for a start, about eight millimetres, less than half the size of the nail on your little finger and is shaped and coloured to resemble a bird dropping, which it mimics with incredible accuracy. The chrysalis is attached on the upperside of a leaf  or to a small twig and is a real challenge to find but once one's eye is in and you know what to look for it becomes slightly easier to find one.

A Black Hairstreak chrysalis on a half eaten Blackthorn leaf

I commenced examining the leaves and stems of the blackthorn bushes on the sunnier side of the track, not really looking above eye level but lower, as usually the chrysalis is to be found there. At first I found nothing and for over forty minutes I examined many likely looking blackthorn leaves and stems with zero success. Somewhat chastened at my lack of success I walked back the way I had come re-checking leaves and stems but still found nothing. Confounded and frustrated I stood looking at a blackthorn clump, letting my eyes idle over the leaves and just where I briefly focused them I saw something, a tiny brown and white blob attached squarely to a shiny dark green blackthorn leaf. Could it be? I moved forward and looked closer, gently tilting the underside of the leaf with my finger. It was. There, at last was one of nature's marvels, a Black Hairstreak chrysalis.

A cathartic moment as I savoured the delight and satisfaction of my hard worked for victory. I stood in a quiet, almost reverential communion with the chrysalis, an apparently dead and lifeless speck concealing the scarcely credible chemical processes taking place inside it, even as I looked on at its hard carapace, that would  eventually split asunder to reveal, in a couple of weeks, a beautiful Black Hairstreak butterfly.

Images of a Black Hairstreak chrysalis showing how well camouflaged and
insignificant it is amongst the blackthorn leaves

I walked on and now with 'my eye in' found another chrysalis rather more cunningly concealed on a stem below a leaf and much less obvious.

I was pleased with that one and determined to find more. I found only one more, again low down, no more than waist height on a blackthorn leaf, illuminated by the afternoon sun. I had been here over an hour and I had found three chrysalises which exceeded all my expectations. Two years ago I found my first and only one, so today I had excelled myself and was pleased.

Many Black Hairstreak chrysalises, up to 80%, are predated before they can emerge as butterflies. It seems a shame that such perfection meets such a fate but nature has no sentiment. The chief predator, I am told, are Willow Warblers, that obviously are not so easily fooled by the cunning disguise and more adept at discovering a chrysalis than myself!

Well at least three have survived and I read that an Upper Thames Butterfly Conservation visit here last week found ten surviving chrysalis so it looks good for the coming short flight season. I do hope so and I will return in a couple of weeks on a sunny morning to find out.