The Amazing Brown Hairstreak Egg Searching Season 2025–26

However, once the festivities were over and egg searches resumed, it was a different story: we made lots of trips but eggs were just not as forthcoming. Although we were still ticking off the occasional new square, we had to work much harder for them than we had before Christmas. So much so that we had only added another eight squares by mid-March and began to wonder if we’d reach 400 before the season finished at the end of the month (once the blackthorn starts to flower, it's impossible to see eggs on the stems).

Our annual search at Morton Stanley Park in Redditch was scheduled for 19 March and I was determined that, after we’d completed it, we’d head over to nearby Batchley and target two squares that we’d searched unsuccessfully on and off over the years. When we arrived at the first of those squares, it was immediately obvious that very little blackthorn habitat was present. The search began tentatively but remarkably, within moments, an egg was found: square number 399. The second square, just across the road, had far more suitable habitat and so the 400th was a given – correct?

Well, half an hour later, and none of the nine searchers had found an egg. Then, suddenly, a cry went up and Gill had found a double! Much celebrating ensued – mini-chocolate eggs were handed out and consumed – we'd reached that magic total of 400!

 The Thursday Streakers (Mike Williams)

 There was still time for a couple more searches and another two new squares were added to the tally. With that, a fantastic egg-searching season drew to a close. We'd found an unbelievable 68 new squares (25 in Worcestershire and 43 in Warkwickshire), giving a final total of 402 squares (317 in Worcestershire and 85 in Warkwickshire).

That raises the question of why we found so many new squares during the 2025–26 season. I think the answer is twofold:

• The Brown Hairstreak, which has been doing extremely well in the West Midlands for many years, undoubtedly had an exceptional egg-laying year in 2025 – our counts at other regular sites were generally well up on average.
• Squares in Warwickshire, where most of this season’s discoveries were made, were largely overlooked by searchers until two years ago – the extent of the species' inroads over the county border had not been realised until recently.

So, what will the 2026–27 search season hold? I can confidently say that we won’t find nearly as many new squares as in the season just ended … but then again, that’s exactly what I said at this point last year!

Feckenham Electricity Sub-station – 2 April 2026

Final seasonal update from Mike Williams

This was our last count for the season, with the blackthorn flowering and even showing leaves in places. Despite the early April date, the first eggs had hatched (another record) – we saw several with a tell-tale neat hole in the middle where the young caterpillar had emerged. This is another example of the impact of our changing climate on species' emergence times and perhaps their chances of survival. We found hatched eggs on bare blackthorn stems, with no sign of leaves on which the larvae need to feed.

Another possible effect of climate change was the large number of eggs found on suckers at the base of a north-facing hedgerow. Generally, Brown Hairstreak favours south- or east-facing hedgerows for egg-laying and it will be interesting to see if this behaviour is a one-off or something that may occur more often.

Overall, it has been a fantastic year for the Brown Hairstreak, with a record number of new 1km squares being added to the distribution map. I was pleased to add one more on my way home: a new square at Hanbury Hall took our total to an amazing 402 for the Forest of Feckenham. This is a real tribute to the volunteers led by Simon Primrose, whose commitment over many years has produced this good-news story for butterflies.