The Brown Hairstreak butterfly (Thecla Betulae) is one of the UK’s most threatened species, currently listed as vulnerable on the GB Red List (2022) and a priority species under the Natural Environment and Rural Communities (NERC) Act (2006). Its population has been in decline due to hedgerow removal and frequent flailing, which destroys the overwintering eggs laid on young blackthorn shoots—the butterfly’s primary food source.

As part of a comprehensive ecological survey, FPCR was commissioned to conduct a Brown Hairstreak survey in an area where records had indicated its presence. Since adult Brown Hhairstreaks spend much of their time high in the tree canopy, egg searches are the most effective method for detecting their presence. These distinctive, bright white, sea urchin-like eggs are typically found on young blackthorn (Prunus spinosa) growth, sheltered and facing west or south.

In February 2025, our experienced butterfly surveyors—Natalie Kay, Oly Sayers, and Rosie Murfitt from FPCR’s Dorking office—conducted an egg search in accordance with UK Butterfly Monitoring Scheme (UKBMS) guidelines. The team surveyed non-flailed hedgerows with suckering blackthorn, successfully identifying 50 Brown Hairstreak eggs across four hedgerows.

This important discovery highlights the significance of preserving and managing hedgerow habitats to support the Brown Hairstreak’s lifecycle. Based on our findings, FPCR will provide tailored habitat management and creation recommendations to ensure this rare butterfly continues to thrive, benefiting a range of local wildlife.

By safeguarding key habitats, we can play a vital role in reversing the decline of this beautiful species and ensuring its future in the UK.