The Purple Hairstreak is a common butterfly, but it is only rarely seen or recorded on a standard butterfly monitoring transect because of its unusual behaviour. It lives in the top of mature oak trees where it feeds almost exclusively on honeydew, and is most active in the early evening. They are only occasionally seen at low level where they might be nectaring on bramble or thistles.
Strawberry Hill was a conventional arable farm until the 1990s when the whole 150 hectares was ‘set aside’ and has not been farmed since. Most of the site is now scrub, dominated by hawthorn and blackthorn with some open areas of grassland. It is the largest area of scrub in central England and an important site for breeding birds especially Turtle Doves and warblers, including Nightingales. When the site came up for sale in 2020, the Wildlife Trust secured the lease and has now successfully raised the funds to buy the whole site.
Several butterfly surveys were carried out in 2020–23, which confirmed the presence of most of the common and widespread species typical of grassland and young woodland. There were also a couple of Purple Hairstreak records, and we assumed that they were breeding in the small number of mature oaks trees scattered across the site in the original farm hedgerows.
The chosen survey route went across the middle of the site and covered 13 oak trees at 11 locations (3 trees were very close together and counted as 1 location). We carried out a survey one evening each week for 9 weeks and saw a total of 58 individual Purple Hairstreak at 8 out of the 11 locations. None were seen at the remaining 3 locations. The peak counts were 17 and 16 individuals on the 18th and 26th July respectively and the peak count at a single location was 7. Although the numbers were not high, we know that on a conventional transect, looking for butterflies at low level in the middle of the day, we would have been lucky to see more than 1 or 2 individuals. The weather in 2024 made surveying difficult with many evenings that were too cool, wet and windy, but we don’t know what effect that had on the overall numbers. When we get the full analysis of local and national Purple Hairstreak records for 2024, we might be able to put our numbers into context.
If you want to monitor a site for Purple Hairstreak there is a guidance note (NG4) and training video on the UKBMS website. Alternatively, you might want to set yourself the challenge of looking for them in your local park or woodland. Ideally you want to select a few mature oak trees on the western edge of a woodland so that you can observe the tree canopy with the evening sun behind you. They are a delight to see chasing each other across the tree canopy even if you only get a distant view through binoculars and end up with a crick in your neck! Prof. Jeremy Thomas, in his book ‘The Butterflies of Britain and Ireland’ wrote: “From the ground they look like a handful of silver coins that has been tossed into the sunlight, and are one of the wonders of the British butterfly season….”
If you do see any Purple Hairstreaks, the County Recorders would welcome your casual records for this elusive and under-recorded species.
My thanks to the Strawberry Hill Farm Butterfly monitoring team Helena, Christina and Lindsey for their dedication and letting my wife Emma and I join them on a few occasions. Thanks also to Chantelle, the Wildlife Trust Site Manager, for submitting the records to the UKBMS website.
