In June 2009, the Reserve and Michael Walter, the former Warden, received nationwide publicity for the record numbers of heath fritillary butterflies found in the woods. Numbers had increased from around 120 butterflies in 2008 to well over 1,000 in 2009. Sadly the high numbers can’t be expected every year, but here is Michael’s report on his butterfly survey in the woods this year, written at the end of July:
Given the appalling spring we endured so recently, it is no surprise that Blean’s famous butterflies failed to appear on schedule this year, with the first ones seen on 14th June, the latest date for 12 years, and peaking on 8th July, the latest since 1991. But, although in the previous six years they had emerged in the second half of May, the historical context is that back in the 1980s mid-June was the norm, and it is perhaps only thanks to climate change that we have recently become used to them appearing earlier. The graph (below) clearly shows a steady trend towards earlier emergence over the past twenty years, abruptly ending with the sudden upturn of the line as it hit the buffers this year.
This year was never going to be an outstanding one for our fritillaries, but it has still managed to rank sixth out of the past thirteen, which isn’t at all bad considering the weather they have had to contend with. The season is virtually over now and any stragglers tend to be very tatty individuals looking extremely washed out, having had most of the colourful scales knocked off their wings.
No colonies actually went extinct, which was a relief, but the performance at most was generally undistinguished, with only one site reaching a peak approaching a hundred. Let’s hope next year brings better news.