Sunday 28 July 2019

A Year in the Life of a Black Hairstreak

The Black Hairstreak butterfly has held a special place in my heart for almost as long as I've held an interest in butterflies. Their specific needs making them a real Northamptonshire speciality coupled together with the elusiveness making them a challenge to study only make the species more appealing to me. The Black Hairstreak was one of the first species of butterfly I made a special trip to see when many years I ago I headed to Glapthorn hoping that I'd bump into someone who knew what they were doing and show me where to see them. As it happens I was in luck and no sooner had I visited the reserve a knowledgeable chap agreed to let me accompany him and he took me for a tour round before showing me my first Black Hairstreak nectaring on a flowing in the infamous third ride! The experiences on this day made a big impression on me, not only did I fall in love with this small but beautiful insect but the seeds were also sown in my mind to study butterflies in much more detail. One of the biggest regrets of my early days is not getting the contact details of this man who took me around (he cut a very distinguished figure in his plus fours, long walking stick and hat with a feather) as I would really like to personally thank him for inspiring me to follow a path that has led to me becoming the Northamptonshire butterfly recorder. For the next few years I visited Glapthorn every year on my annual pilgrimage to admire this butterfly and then I decided once I'd had my fix for the year I'd try and find some at a different site. After some reports of Black Haistreaks being seen at Fermyn Country Park I checked that area out for a few years too. What I really wanted though was to discover some for myself and after my local patch at Grange Park got scraped and made into a couple of warehouses I decided to make Salcey Forest my new area of study. I'd already had plenty of conversations prior to this with Doug Goddard the previous butterfly recorder and listened intently to him reminiscing about the many Black Hairstreaks that used to be seen around Salcey before their slow demise and considered extinction at the site so I had to make find Black Hairstreaks a priority. I spent day after day during the winter months searching for suitable Blackthorn stands and clearings before staring over the same areas during the butterfly's flight time hoping to see one. Then in 2015 I struck lucky when during a quick early morning visit I saw a small butterfly flit from a Blackthorn bush and onto a Sallow. A quick photo with the bridge camera zoomed right in showed the black dots along the outer edge of the hindwing proving by some amazing piece of luck I'd somehow managed to do it and find them once again in Salcey! Even luckier the butterfly then took off and descended to vegetation within reach of the SLR so here in the photo of the first one seen in Salcey for a fair few years!

Black Hairstreak, Salcey Forest 2015
 One thing that we are very lucky to have here in Northamptonshire is the dedicated band of butterfly recorders and after the news broke about the Black Hairsteaks being rediscovered in Salcey Forest a great team then searched and searched over the next few years and with their help we've learnt a great deal about their spread around the forest. The amazing Black Hairstreak season in 2018 saw some incredible numbers in their strongholds throughout the county and I realised this also offered the best opportunity I was probably going to have to study the early stages. I had already spent a couple days during each winter for 4 years leading up to this looking for Black Hairstreak eggs without success so I already knew that it would be a challenge even it had been the best season on record but I decided to accept the challenge all the same. Of course looking for early stages does have it's advantages, you don't need good weather, you get a tremendous sense of self congratulation when you find something and it's something butterfly related you can do in mid December when thoughts of June seem to be a distant memory. Personally I also find methodically going through branch over branch from tree to tree extremely relaxing but I know others baulk at the idea! The highest concentration of Black Hairstreak adults in 2018 unsurprisingly came from Glapthorn Cow Pastures and as this site is the first place I saw the species I decided to concentrate my efforts here.

I started my first search during a wet day on the 28th of November in 2018. I searched all the Blackthorns along rides 2,3 and 4 along with the adjacent rides too. I have to admit I didn't realise how many moths lay their eggs on Blackthorns too and so often I thought I'd found one only to be disappointed once closer examination with the hand lens proved it to be a moth egg or an bud breaking on the branch. Eventually while searching again in ride 3 I searched some new Blackthorn growth and out of the corner of my eye I noticed a Blackthorn a bit deeper in with a small circular disc tucked under a thorn. Without looking through the hand lens I realised I'd finally found one! Below is the photo. The egg was situated on new growth approx 6ft high.

Black Hairstreak egg, Glapthorn Cow Pastures 28/11/18
After this sighting there was a bit of a gap in searching as the long awaited butterfly recording data repatriations poured in which meant I had to spend most of my days off on the laptop collating and analysing it all. I did get in a visit to Fermyn Country Park though as we had a conservation work party there on the 17th of March in 2019. As I hadn't had an opportunity to explore the site over the winter I arrived early in the morning to get a few hours searching in before the work party started. Despite searching all the new growth I failed to find any but as I was about to give up I searched some more out in the open Blackthorn and in the fork of a mature tree in a fork about 5ft up I discovered an egg casing! It wasn't a surprise that any discovered egg would have hatched as Spring was definitely well under way at this point but despite a very thorough search I couldn't find what would have been a tiny 1st instar larva.

Black Hairstreak egg (hatched), Fermyn Country Park 17/03/19

Over a month later on the 28th of April I visited Glapthorn again but this time to look for larvae. I straight away went to the area I'd found the egg in but despite finding the egg successfully hatched I couldn't find any caterpillars on the branch. I kept checking along the stand of new Blackthorns and approximately 4 feet to the left of the egg on a different tree I found a larva tucked inside a leaf approx 3ft off the ground.

Black Hairstreak Larva, Glapthorn Cow Pastures, 28/04/19
I then returned to the same area of Glapthorn a few weeks later on the 17th of May with the hope of finding the last early stage left to see but despite a thorough search I couldn't find any pupae. I did find this larva below though which after closer inspection showed it had spun a silk thread attaching itself to the leaf and was in preparation to pupate! You may have to open the image and zoom in to see it.

Black Hairstreak Larva (ready to pupate), Glapthorn Cow Pastures 17/05/19
I must admit at this stage a degree of anxiety had crept in that (despite the pupal stage being the easiest to find in the wild) after coming this far I wouldn't be able to find any pupae so I had to make sure I could get back here as soon as I could to see if the larva that looked to be pupating had actually succeeded. I went back on the 19th of May and I was very surprised that the larva in question was still on the leaf but still very much in it's larval stage. I was a little dismayed by this to say the least as I knew that the pupal stage was the one they suffer the most predation in and I couldn't get back in here for another week due to work so it may well be snapped up by a bird before I could return. Despite this set back, and the fact I had also committed myself to another butterfly survey in the county so I didn't have much time, I decided to carry on searching as surely there must be some more in here! I spent a good hour checking all the Blackthorns in the ride but it was in vain. I felt the clock ticking and I was running out of time so I decided to head back to the entrance of the reserve but checking as much of the Blackthorn as possible along the way. As I approached the 2nd from last ride I looked at my watch and decided that at a push I could give it a half an hour search so I started looking. A sense of defeat had by now crept in and I half heartedly trawled through the branches. I should add at this point that the reason Glapthorn Cow Pastures is so good for Black Hairstreaks is because of the superb team of Wildlife Trust staff and a dedicated band of volunteers who do great conservation work here managing the Blackthorn. Laying the Blackthorn promotes fresh growth and it was while checking the twigs on the outer edge of one of these young bushes I noticed the tell tale bird dropping camouflage of a Black Hairstreak pupa nestled on the top of a thorn and tucked inconspicuously under a leaf. The sense of relief I felt is almost impossible to put into words but by now I only had 20 minutes spare so I ran to the car to grab the tripod from the boot to get the photo below. It was quite a moment for me and was the culmination of a steep learning curve I had to take to learn more about this incredible butterfly and it's life cycle. My day got even better as after this as I had to travel to a site in Rockingham Forest to carry out a butterfly survey where I saw something else I'd always wanted to see, but more about that another day!

Black Hairstreak Pupa, Glapthorn Cow Pastures 19/05/19
The following week on the 26th of May I just had to go back to Glapthorn while I had a couple of spare hours in the morning to see if the larva I'd found in the process of pupating (the one on the 5th photo) had succeeded. I walked up to where it was and instantly saw it surprisingly out in the open.

Black Hairsteak Pupa, Glapthorn Cow Pastures 26/05/19

Black Hairstreak Pupa, Glapthorn Cow Pastures 26/05/19
This pretty much brings the story to a close, except of course I couldn't do all of the above and not see the adults during their next season. Of course the numbers were lower than their spectacular season the previous year but they were still flying in good numbers so here are a few photos of the 2019 season adults. It was the culmination of an enjoyable journey tracking this insect all the way through it's life cycle. All I need to do now is try and work out which butterfly I should try and study this winter!
Black Hairstreak, Glapthorn Cow Pastures 09/06/19
Black Hairstreak, Glapthorn Cow Pastures 23/06/19

Black Hairstreak, Glapthorn Cow Pastures 23/06/19


1 comment:

  1. Excellent most interesting and well put together piece of information.


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