The rise and rise of the Brown Hairstreak butterfly

When last winter’s egg-searching season finished in April, we had confirmed the presence of the Brown Hairstreak in 42 new, previously unrecorded, OS grid squares. This was easily a record number for one season for the Thursday Streakers – beating the 25 new squares seven years ago – and I confidently predicted that we not only would never reach that total again but would be unlikely to ever get close to it. Well, how wrong I was!

This year’s searching season got off to an early start with adult sightings in August at two new sites in the Pershore area: Tiddesley Wood and Mike’s Meadow. The first new egg square followed soon after in September, near Walcot Lane in Pershore, and then the egg searching season truly got underway in October, with new square discoveries coming thick and fast. It wasn’t even a case of finding a new square or two every time we searched, we were finding four or five on some days, peaking at a record (for us) on 13 October when Gill and Geoff Thompson and I found eggs in six previously unrecorded grid squares around Studley, Sambourne and Mappleborough Green. Eggs were then found in a number of locations in and around Tiddesley Wood for the first time, after many unsuccessful years of searching there, adding four more new squares in the process.

We now had the bit between our teeth and, with the arrival of November, there was still no let-up in new discoveries. So much so that by 25 November we had not only equalled last year’s new square total, but smashed through it. Gill’s discovery of eggs near Great Alne and in Abbey Fields Nature Reserve in Alcester registered, respectively, our 42nd and 43rd new squares of the season. Not only had we beaten last year’s 'unreachable' total, but we’d done so with over four months of the searching season still remaining! Further finds in December have subsequently boosted our total to 52 new squares.A few amazing stats and records:

• We have now recorded Brown Hairstreak in 386 OS 1km grid squares across east Worcestershire and west Warwickshire (having only recorded the 300th on 12 December 2024).
• We have now recorded 86 new squares in the 2025 calendar year.
• Brown Hairstreak has now been recorded in 74 west Warwickshire squares, up from only 14 just three years ago.

There are undoubtedly many reasons for this apparent sudden upsurge in this butterfly’s fortunes, not least the explosion of the population across the county border into Warwickshire around Mappleborough Green and Studley, especially into the extensive Blackthorn plantations on land owned by the Heart of England Forest around Spernal. However, what is certain is that the species is responding very favourably to our warming climate, along with various farm stewardship schemes, and faring exceptionally well in the Blackthorn-rich landscapes not only here, in this part of our region, but in many other areas of the country too.

Photos:

The search in progress by Mike Williams

Discovery in the 43rd square by Simon Primrose