The threatened Brown Hairstreak butterfly’s range in South-west Wales has more than halved in the last decade, a new study by Butterfly Conservation South Wales Branch reveals.
To help reverse this decline it recommends that blackthorn hedges suitable for this butterfly should be not be flailed every year but should be left uncut at least every alternate year.
The study from Butterfly Conservation South Wales branch shows that smallholdings are now the main refuges of the rare the Brown Hairstreak butterfly, which is just about hanging on in South West Wales.
The Brown Hairstreak is listed under the Environment (Wales) Act 2016 as a species of principal importance for the purpose of maintaining and enhancing biodiversity in Wales.
Richard Smith of the South Wales Branch of Butterfly Conservation said: “The adult butterflies live mainly in the tree canopy (typically Ash) but lay eggs on young shoots of low-growing Blackthorn in the hedges below. The eggs remain on the Blackthorn shoots through the winter, with the caterpillars hatching the following spring. Mechanical flailing of a hedge or scrub during the autumn and winter period has been shown to remove 80-90% of eggs. If this continues year-on-year, the ever-decreasing population vanishes within two or three years.”
Hedging experts advise that once every three or four years is a suitable interval for trimming hedges. Despite this, mechanical flailing of most farm hedges every autumn/winter seems to be common practice. This annual flailing is far more intensive than traditional labour-based management, in which hedges were laid every few years on rotation across the farm.