White-letter day on Banstead Heath

November 2023

On a bright and sunny day in November, the Conservators warmly welcomed Bill Downey to Banstead Heath in what was a modest but significant tree-planting event in Surrey.

Bill is the Species Champion for the White-letter Hairstreak butterfly at Surrey and SW London branch of Butterfly Conservation.  In his role, Bill not only helps to survey for populations of the butterfly but also creates habitat for the species by planting its sole larval food plant, Elm trees.

Since the accidental import of Dutch Elm Disease, the disease, spread by Elm bark beetles, has devastated English Elm (Ulmus minor vulgaris) populations across the UK. The once common and much-loved English Elm (not in fact a tree indigenous to Britain) is strongly associated with the landscapes of Constable. Although the disease does not in fact kill the trees, which will sucker up again from the roots, it has resulted in the loss of virtually all mature flowering and fruiting elm.

The loss of so much elm habitat has decimated populations of the White-letter Hairstreak which it is estimated has declined by some 96% since the 1970s – more than any other British butterfly species.

Since the 1980s, as a result of specialist breeding programmes mainly in Europe, scientists have created new, resistant Elm varieties that are not affected by the disease. Elm is an important component of the British landscape and the re-introduction of resistant trees will permit the many species which rely on the tree to survive – not just the White-letters.   

Bill chose Banstead Heath as a good location for planting elms. Last summer he found White-letter Hairstreaks on the large Wych Elm (Ulmus glabra) growing on Mogador Road and also on the Wych Elms on the A217 at Lower Kingswood. The species should easily be able to spread from these locations and in time the Heath should support new breeding populations, so he kindly donated seven trees to plant on Banstead Commons.

It was a straightforward start to the day.  The team agreed on the best locations to plant the new trees and it wasn’t too long before the first three European White Elms (Ulmus laevis) were safely in the ground. This is not a true resistant elm but a species in which a chemical in the bark repels the vector beetles.



Image:  Conservator David Hatcher (left) and Bill Downey planting one of the European White Elms on the Heath.


It was when the small team of three moved to the next location to plant the other two cultivar species that they got distracted!    The spades were down and before we knew it three sets of eyes were looking for Brown Hairstreak butterfly eggs on the Blackthorn (Prunus spinosa).  The Brown Hairstreak wasn’t picked up on the inaugural transect season this year but we know the species would be present on the Heath with Blackthorn growing abundantly across the site.

Success!  Three eggs were found in short succession and with reassured hearts and minds, the small team once again concentrated on the task ahead, planting the last four Elm trees (three Ulmus minor Ademuz and one  Ulmus Lutece).  Ademuz is an exciting new cultivar developed in Spain. Most of the disease resistant varieties do not look anything like the billowing, ‘immemorial’ elms of memory, but there is hope that with Ademuz this will change.


Image: Brown Hairstreak egg on Blackthorn

With the new trees firmly in the ground, the Banstead Commons Conservators would like to say a massive thank you to Bill Downey and Butterfly Conservation for working with us to enhance our landscape for butterflies.   The more informed we are about the habitats and species in our care, the more work that can be done to protect, preserve and enhance our landscapes for the benefit of wildlife and future generations to enjoy.

We look forward to recording our first White-letter Hairstreak during our butterfly transect in a few year’s time –  working in conservation, it is always advisable to plan in tree time, years rather than hours!


Image: one of the Ulmus Lutece trees

Banner photograph of the White-letter hairstreak butterfly by Trevor Sears

Article written by Lucy Shea and edited by Bill Downey.