The Rarest Hairstreak 8th June 2020

I took Tweedy to see and photograph Black Hairstreaks at Bernwood Forest on Tuesday, the last day of the hot spell of weather we had so enjoyed. I am delighted to say we were successful which is just as well as he had travelled all the way from his home in Essex.

It was good to see him as it has been a fair few years since we last met but it felt as if we had only parted the day before

The weather on Wednesday then took its inevitable downward course for the rest of the week, turning colder, cloudier and occasionally wet. I decided that despite this I wanted to see a bit more of Black Hairstreaks after my earlier experience but baulked at going back to Bernwood as it tends to get a bit crowded there with butterfly enthusiasts, due to being the best known location in Oxfordshire to see Black Hairstreaks.

I know of another wood that contains Black Hairstreaks and tends to be far less populated by butterfly enthusiasts so decided to visit there on Sunday 7th of June. I left home at about nine to make the forty minute drive to the wood and all seemed in order as the sun was shining and it looked to be a good day for seeking out butterflies and Black Hairstreaks in particular.

When I got to the wood at just before ten my mood of optimism changed as light cloud had rolled across the sky and any sun was now only apparent in very short spells of no more than a minute. Needless to say nobody else was foolhardy enough to take the chance to venture out for butterflies and I had the wood to myself but of butterflies there was, predictably no sign.

At just after ten it was chilly on leaving the car, courtesy of a brisk northwest wind and I was far from optimistic about having any success as I entered the wood. In fact I thought I had badly miscalculated. My location of choice in the wood and where I considered I was most likely to see a Black Hairstreak was a very narrow bridleway running between the edge of the wood and a broad hedge of blackthorn, in parts only head high and through which wild privet, dog rose and bramble grew. The sickly sweet scent of the privet flowers hung, tantalisingly faint, on the air.

The privet would be the key to any success, as in this wood Black Hairstreaks will come down from the higher trees to nectar on the privet flowers as a supplement to supping honeydew from the surface of leaves up in the trees

The long summer grasses were wet underfoot from last night's thunderstorm, flattened in places by the force of the rain but now the earlier sun had dried the blackthorn and if and when it reached the grass that would dry too

Having already selected what I considered a likely spot to see any hairstreak that took to the air along the hedge, all I could do was stand and hope, something Black Hairstreak enthusiasts are no strangers to! It is almost impossible to find them unless they move or are nectaring on a privet flower. I stood wishing the sun would become more permanent but it rarely permeated the light cloud and when it did it was all too brief, just a couple of minutes at the most before it was obliterated by the constantly moving banks of clouds.

Birdsong was ringing throughout the wood behind me. The rich tones of a Garden Warbler spilled out, a tumbling cascade of mellow notes delivered just that bit faster than the very similar song of a Blackcap. More distantly the wistful song of a Willow Warbler could be heard when the Garden Warbler lapsed into a temporary silence.

A family of Magpies had just fledged and the young were scattered in the tops of the small trees above me. Invisible to the eye but betraying their presence by a continuous series of grating, staccato and conversational calls, sounds that one never hears from an adult bird but unmistakeably were those of a magpie. 

For a full forty five minutes I stood and waited, willing the sun to penetrate the cloud. Occasionally it did and I felt the warmth on my face and the sudden illumination cast brief shadows along the bridleway, raising hopes it might stimulate a hairstreak into movement. A flicker of brown briefly jinked amongst the leaves on the top of the hedge. A butterfly for sure but it was too big. It was a Meadow Brown, which prostrated itself on a leaf with wings wide open  to absorb whatever warmth it could. Butterfly expert Neil Hulme succinctly called this behaviour 'pancaking' where the butterfly holds its wings wide open and flattened to heat its body so it can fly.

A Meadow Brown 'pancaking'

Another flicker of movement came but this time it was a Large Skipper, that copied the Meadow Brown and perched immobile with wings held open to absorb whatever rays of sun periodically shone on the hedge. Large Skippers have a shape akin to that of a jet fighter with triangular swept back wings and, like a jet fighter, they are ready to scramble at the slightest notice to intercept an intruder. In the case of the skipper this being other butterflies and insects, no matter how large or small.They are fearless and relentless in the defence of what they consider their private airspace.

A Large Skipper awaiting the next intruder to its airspace

An hour and a half later and finally an extended burst of sunshine shone down on the blackthorn but no hairstreak had appeared to nectar on the privet flowers. No movement. Nothing. Disappointed I walked to the end of the bridleway and turned to walk along the country lane that bordered the other side of the hedge.

The lane with blackthorn hedgerows on either side

It was less sheltered here and gusts of wind periodically shook the hedge. It was now past eleven thirty and still there was no inkling of any hairstreak action. I found a Small Tortoiseshell nectaring on some privet flowers, doubtless stimulated into action by the sun. Suddenly a much smaller, dark brown form came jinking past me along the hedge at face level. A Black Hairstreak! It settled briefly on a blackthorn leaf, tilting its closed wings so they received the full benefit of the sun but no sooner had it done so and I raised my camera than the Small Tortoiseshell fluttered too near to it and the two butterflies spiralled away before they broke off their confrontation and the hairstreak fluttered away over the top of the hedge to the far side. So near but yet so far. I was utterly frustrated as it was impossible to follow the hairstreak  as I would have to go back along the lane, around the hedge to the other side and by the time I got there it would be impossible to find the tiny insect.

I walked the length of the hedge and back again but there was no sign of any more hairstreaks but a few Meadow Browns were now flying, which was cause for optimism and the sun looked like it was here for an extended period. My hopes remained intact, just about, and I turned to walk, for a third time along the lane, closely examining the hedge and privet flowers on my right as I went.

Halfway down I found what I was looking for, although I so nearly missed it. Partially obscured, a tiny triangle of mouse brown wings with a bright orange border to the underwings was sat at just above head height on top of a small spike of waxy white privet flowers. It was another Black Hairstreak and in perfect condition. At last I had a good view of one and more to the point it looked like it was here to stay for a while, as it was avidly casing the privet flowers for nectar, then fluttering to another spike of flowers to repeat the process.

It moved with almost imperceptible tiny steps, meticulously examining each tiny flower of the spike, walking up, down, then around until it had covered every individual flower. Other insects were also coming to the flowers and I prayed they would not irritate the hairstreak and cause it to fly off. Disaster nearly struck when a bumble bee, fully justifying its name barged into the hairstreak and for a heart stopping moment the butterfly fluttered away but then circled around to come back to an unoccupied spike of privet flowers in front of me. 

Note how the hairstreak's left antenna is sensing and assessing the bumble bee's movements

For half an hour I watched it, enthralled and noting how it used its antennae to guide its way around, lowering them as it made its way across the flowers. Does it use them to sense the nectar or is it just to guide it across the uneven surface of the flowers? For a brief spell it perched on a privet leaf as if sated with nectar but then it was soon clambering back to the flowers for more.

They are an exquisitely marked and attractive insect, the underside of the mouse brown hindwing bears a broad band of deep orange at its outer margin, then a narrow border of black and white at the extreme edge of the wing, with two tiny protuberences called tails. The inner edge of the orange band shows a dotted row of black and white spots and across the centre of the wing is the irregular thin scribble of white from whence the butterfly derives its name. Look even closer and the antennae and six legs can be seen to be banded alternately black and white.

Judging by the way the tails are angled upwards this is probably a female

I was pleased as punch that my persistence had paid such a handsome dividend from what was looking to be a lost cause.

I never saw it go as  I took my eye off it for fraction of a second and when I returned my gaze to the privet flower it was gone and was nowhere nearby.

I walked back along the road and saw another that also settled on a privet flower but for seconds only before a gust of wind persuaded it to disappear. It really did not matter as I was totally satisfied with this year's Black Hairstreak encounter.

At just after half past twelve the sun retreated and the hedge became cold and inhospitable once more and I knew that my chances of finding any more Black Hairstreaks were virtually nil. I headed for the car, delighted with my thirty minute audience with a Black Hairstreak, Britain's rarest hairstreak.