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Have you ever seen a brown hairstreak? I mean the butterfly that is, and not the result of a close encounter with a seagull on your summer holidays!

Very few people have; even devoted lepidopterists (a person who studies butterflies and moths) may go years without seeing one. For most people living in the Midlands, the brown hairstreak (Thecla betulae) is an exceptionally rare butterfly and is a UK Biodiversity Action Plan priority species for conservation due to its continued decline. The nearest reliable colonies require a journey across county borders if you are to stand any chance of catching a glimpse of one.

Every August and September, Grafton Wood near Flyford Flavell in Worcestershire, Bernwood Meadows near Oakley in Buckinghamshire and Otmoor, located a few miles north-east of Oxford, witness annual pilgrimages by butterfly enthusiasts keen to observe first-hand the beauty of a brown hairstreak. But many will go home disappointed since this butterfly can be frustratingly elusive even for the seasoned observer.

A female brown hairstreak with her distinctive golden flashes on her upper forewings basks at the base of a sheltered hedgerow at Grafton Wood in Worcestershire.

A female brown hairstreak with her distinctive golden flashes on her upper forewings basks at the base of a sheltered hedgerow at Grafton Wood in Worcestershire.

 

Winter egg searches undertaken in the late 1990s by volunteers at Grafton Wood discovered that the butterfly is much more widely distributed than first thought. Similar searches around Otmoor led to discoveries of eggs in Oxford, approximately 7km from the core site.

The egg search is on…

Despite the discoveries of eggs found beyond the core areas in Worcestershire and Oxfordshire, the species is absent from most of Warwickshire even though the caterpillar foodplant blackthorn (Prunus spinosa) is common in our hedgerows. The explanation for the butterfly’s absence is simple. The female lays her eggs on the previous year’s blackthorn growth. They remain here throughout the winter before the caterpillar emerges to feed on the first leaves to appear in the following spring. Unfortunately, regular winter hedgerow cutting removes the eggs before they can hatch. With the increasing use of mechanical flails, the butterfly, or rather its eggs, don’t stand a chance. The result is regional extinction.

A small colony of brown hairstreaks can be found at Ryton Wood Meadows (Butterfly Conservation Warwickshire) near Coventry, their presence the result of an introduction a few years ago. While the colony here appears to be stable and self-sustaining, only a handful of adult butterflies are observed here each summer. But what this colony does illustrate is that appropriate management of blackthorn hedgerows can make a huge difference in the ability of the species to survive and thrive, even in relatively small patches of suitable habitat.

An egg of a brown hairstreak butterfly with its distinctive honeycomb surface. The eggs are usually laid singly between the fork of a branch of a low growing blackthorn bush.

An egg of a brown hairstreak butterfly with its distinctive honeycomb surface. The eggs are usually laid singly between the fork of a branch of a low growing blackthorn bush.

 

A home for hairstreaks in the Heart of England Forest

Tantalising records started to emerge back in 2010 when a brown hairstreak was reported to have been seen at King’s Coughton, north of Alcester. With the nearest colony at Grafton Wood approximately 12km away, it is not implausible that the butterfly could, given the chance, make its way into Warwickshire breeding as it travels on isolated patches of suitable habitat, moving through the countryside towards the Heart of England Forest. Further surveys between 2011 and 2017 resulted in more eggs being discovered in several locations along the Warwickshire/Worcestershire border.

Spot the eggs? There are two eggs visible in this photo but searching for eggs while the leaves are still present on the larval foodplant blackthorn in late summer is hard work and very time consuming. By mid-winter, the pure white eggs are much easier to spot making winter egg searches the most effective way to prove the presence of the brown hairstreak.

Spot the eggs? There are two eggs visible in this photo but searching for eggs while the leaves are still present on the larval foodplant blackthorn in late summer is hard work and very time consuming. By mid-winter, the pure white eggs are much easier to spot making winter egg searches the most effective way to prove the presence of the brown hairstreak.

 

Then, last Autumn, four brown hairstreak eggs were discovered at Netherstead, near Spernal. On the 10th January more eggs were found 3km away. Could we be witnessing the colonisation of the Forest as a result of sympathetic hedgerow management taking place? Could this be the beginnings of a potential new colony similar in size to the one at Grafton Wood? The Heart of England Forest certainly has all the ingredients that the butterfly needs for this to become a reality.

So with the potential colonisation of the Forest by a new species, the Heart of England Forest is working closely with Butterfly Conservation to discover more about this enigmatic butterfly. Further surveys are planned, alongside training on how to find and correctly identify the tiny eggs. It is hoped that this, combined with a better understanding of the species needs and appropriate hedgerow habitat management, will in time give visitors to the Forest an opportunity to experience that special moment when they see their first brown hairstreak for themselves.

By the time sloe berries, the fruit of the blackthorn, have become plump and juicy in late summer, the last female brown hairstreaks of the year will have finished laying their eggs.

By the time sloe berries, the fruit of the blackthorn, have become plump and juicy in late summer, the last female brown hairstreaks of the year will have finished laying their eggs.

 

If you would like to find out more about butterflies and other wildlife found in the Heart of England Forest, why not become a Friend of the Forest to receive our spring 2019 magazine. Published twice a year, our magazine contains a wealth of articles and news about the people and wildlife of the Forest. https://www.heartofenglandforest.com/get-involved/become-a-friend-of-the-forest/

If you would like to take a more pro-active role by becoming a volunteer and helping with our wildlife surveys, then please get in touch. Email volunteer@hoef.co.uk. We would love to hear from you.

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