Brown hairstreak butterflies thrive in parts of south Wales

Conservationists report record numbers of brown hairstreak eggs in Carmarthenshire's Tywi valley after partners reduced annual hedgerow flailing and planted extra blackthorn.

Landowners and conservation partners in parts of south Wales have allowed hedgerows to grow more naturally, and volunteers have recorded unusually high numbers of brown hairstreak butterfly eggs this winter. The species lays eggs only on young blackthorn shoots, which are removed by annual mechanical flailing. Populations in the Tywi valley fell over the past decade as hedgerows were cut back or removed. Work with the National Trust and the South Wales Trunk Road Agent reduced routine trimming and added blackthorn plantings to protect egg-laying habitat. Key findings: - Volunteers surveying hedgerows in Carmarthenshire's Tywi valley found record numbers of tiny white brown hairstreak eggs during December and January searches. - Protected sites reported about a 50% rise in egg numbers this winter compared with recent years. - A nearby cluster of fields that was later “severely flailed” saw egg counts drop from around 60 annually to just four. - Brown hairstreaks lay eggs exclusively on young blackthorn shoots, which are removed by mechanical flailing. - The National Trust and the South Wales Trunk Road Agent reduced hedgerow trimming schedules and planted additional blackthorn to safeguard sites. Summary: The increased egg counts indicate improving local conditions for the brown hairstreak where hedgerow trimming was reduced and additional blackthorn established. Butterfly Conservation has said it does not want to prevent hedgerow management but is promoting less frequent trimming and other habitat measures, and volunteers will continue annual surveys in the valley. Undetermined at this time.