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Brown Hairstreak

Projects - Brown Hairstreak survey & management

West Williamston Nature Reserve is owned by the National Trust and managed by the Wildlife Trust of South and West Wales.  It is situated on the confluence of the Carew and Creswell rivers not far from Carew Castle.  Deeply indented with tidal creeks, which were excavated over several hundred years as a result of limestone quarrying, the narrow ridges and tidal islands left behind now support a rich range of calcareous grassland and scrub woodland communities.   Scarce plants include the bee orchid and marsh mallow.  

The foreshore, and to a lesser extent the tidal islands contain dense areas of blackthorn which supports the largest known colony in Pembrokeshire of the Brown Hairstreak butterfly.  
brownhairstreak The brown hairstreak is a late flying, very elusive butterfly, spending much of their adult life in the canopy of an ash or sycamore.  Very few butterflies hatch per kilometre.  To aid mating they use “master trees”, particularly ash trees growing near to the basin of the countryside that contains the colony. Males perch on the master tree and as females emerge they fly to the tree to mate.  The females lay their eggs into September and by counting the eggs, white, bun shaped and about the size of a pinhead, that we can assess the size of the population.  
Eagle eyed volunteers have turned up to brave the elements for the annual winter egg count since 1996.    The numbers of eggs found has fluctuated each year between less than forty to several hundred. The most recent survey, conducted in December 2004 revealed 125 eggs, which although a steady increase overt the previous two years (double that of 2003) falls short of the larger counts recorded in the past.

Management is necessary to maintain the blackthorn in a condition where it continues to provide suitable habitat for the butterfly to lay its eggs.  The Wildlife Trust organises a program of works throughout the year, which includes blackthorn management over the winter months at West Williamston.  An enthusiastic bunch of volunteers led by the Wildlife Trust have spent a number of days at West Williamston over this past winter in a concerted effort to make the blackthorn more attractive to female brown hairstreaks.  We will have to wait for the result of the 2005 count to see if this has been successful.

Chris Lawrence, Wildlife Trust Officer for Pembrokeshire