The London Environment Strategy - overview

White-letter Hairstreaks in Wandsworth, Lambeth and Southwark

Summary

Detailed surveys of the presence of elm trees and the White-letter Hairstreak butterfly have shown that it is more widespread in the Inner London Boroughs of Wandsworth, Lambeth and Southwark than previously thought.

It is present throughout the boroughs, though never in very high numbers. It is difficult to spot, and probably even now remains under-recorded.

Introduction

The Inner London Boroughs of Wandsworth, Lambeth and Southwark fall within the area of the Surrey & SW London Branch of Butterfly Conservation (part of the old Vice County 17 used for recording purposes).

Not much is known about the distribution and abundance of the White-letter Hairstreak in these boroughs. It is an elusive butterfly, spending most of the time at the top of elm trees (its larval food plant) and only flying when it is sunny and still. It is rarely present in large numbers, and only occasionally comes down to lower levels to nectar. It is unlikely to be seen by casual observers, and transect walks are known to be a poor way of monitoring numbers.

This note describes a study of the White-letter Hairstreak butterfly in 2016 and 2017 by volunteers from the Surrey & SW London Branch of Butterfly Conservation (see www.butterfly-conservation.org/surrey). Although the study covered a larger area, this note focuses on the three Inner London Boroughs. Bill Downey led and coordinated the work.

Status of the White-letter Hairstreak

There are few records of the White-letter Hairstreak in Wandsworth, Lambeth and Southwark, and it has probably been under-recorded here (and elsewhere) in London for many years.

In his book, “The Butterflies of the London Area” (1987), Colin Plant says that the White-letter Hairstreak has always been uncommon - and very local - in the London area. It is shown as absent from Lambeth and Southwark in the 1980-86 period. A single colony is reported in Wandsworth, in Battersea Park: this has been there since 1940 or earlier and remains to this day. Plant mentions the colony as “thriving on three mature specimens of Exeter Elm Ulmus exoniensis, a cultivar of the Wych Elm”.

In the whole of VC17, the butterfly was only recorded in five tetrads (2km x 2km grid squares) in the period 2007-2015 (see below).

More recently, there has been evidence that the White-letter Hairstreak has been making a comeback: in 2016, it was recorded in 24 tetrads. In 2016, there were 165 records of the butterfly in VC17, up from 44 in 2015. This could be due to increased recorder effort, because the 20- and 30-year occupancy trends remain negative (see https://butterfly-conservation.org/files/annual-report-2016b.pdf). Accordingly, it is a High Priority species in Butterfly Conservation’s South East Regional Action Plan.

Records of the White-letter Hairstreak in VC17 for 2007-2015 (left) and 2008-2016 (right)

The White-letter Hairstreak is a priority species for the Southwark Biodiversity Action Plan (see http://www.2.southwark.gov.uk/downloads/download/287/southwark_ecology_and_biodiversity_downloads). It is also on the London Biodiversity Action Plan Priority Species list, last reviewed in 2007 (see http://downloads.gigl.org.uk/website/London%20BAP%20Priority%20Species%20List%202007.pdf).

Methodology

The study followed - and extended - the approach taken by Liz Goodyear and Andrew Middleton of the Herts & Middx Branch of Butterfly Conservation in their 2007-2009 project (see http://www.hertsmiddx-butterflies.org.uk/w-album/index.php).  

Since the White-letter Hairstreak is a canopy species, only rarely (and fortuitously) found on the ground, it has to be looked for in a different way to most other butterflies. The method is to first locate suitable elm habitat and then search for the butterfly during its flight period. Identification is principally via the ‘jizz’ of its distinctive flight and behaviour, although with binoculars it is possible to discern its triangular shape and the characteristic “W” marking on the underwing.

The White-letter Hairstreak only lives on elm (as larva and adult) and has a strong preference for breeding on flowering trees. Our database of elm locations therefore just records substantial trees or large stands. It is not useful (or practical) to record every piece of small, suckering elm.

Possible elm locations have been obtained from a variety of sources: from botanical records, from previous White-letter Hairstreak sightings and from the local knowledge of people involved in conservation. Borough ecology officers were also kind enough to supply information from their tree databases. All of the locations in our database have been ‘ground-truthed’ – most easily done in spring when the fruiting elms stand out in the treescape.  

Notes are taken for each record on:

• The likelihood of detecting the butterfly at that location - for which it is necessary to be able to view the elm canopy. Detection is almost impossible if trees are in dense woodland or if the canopy is otherwise obscured.
• The species of elm, which is important as the use of trees for breeding by the butterfly does vary for different types of elm. Identifying elm however is notoriously as the different species are variable and frequently hybridize.
• Approximate height and condition of the tree.
• An eight- or ten-figure grid reference

The same trees can then be surveyed for adult butterflies in the late June/July, ideally on sunny days with little wind.

English Elm in fruit

Fruiting elm tree in Battersea Park, 31 Mar 2017

Types of elm

• English Elm (Ulmus procera or Ulmus minor var. vulgaris) is widespread through South London but, as all trees are clones only spreading by suckering, it is highly susceptible to Dutch Elm Disease (DED) and may not reach flowering age before succumbing. Where it suckers up into large stands however it is possible to find the butterfly.
• Wych Elm (Ulmus glabra) also occurs throughout South London although its distribution is patchy.  It is susceptible to DED but spreads by seed and so has a higher resistance than English Elm. There are still many large, flowering trees in places and the Wych Elm is probably the favourite native host for the White-letter Hairstreak.
• Smooth-leaved Elm (Ulmus carpinifolia or Ulmus minor var. minor) is the third native species present in the area. It spreads both by seed and suckering but is only locally abundant in a few places, e.g. on Tooting and Wandsworth Commons where there are some large stands and trees. This tree also hosts the butterfly.
• Dutch Elm (Ulmus hollandica) is a naturally occurring hybrid of Wych Elm and Smooth-leaved Elm and has a degree of resistance to DED. It is a variable tree and not easy to identify.
• Huntingdon Elm (Ulmus hollandica ‘Vegeta’) is a cultivar of Dutch Elm which was widely planted in the past in streets and parks and although still susceptible to DED, has considerable resistance to it. A mature, 70 to 80 foot elm will probably be a Huntingdon. Some trees can still be found in South London and are likely to support a colony of the butterfly.
• Ulmus ‘Sapporo Autumn Gold’ is a cross between Siberian Elm (Ulmus pumila) and Japanese Elm (Ulmus japonica) and was the first of the disease resistant cultivars. It was widely planted in the 1980s, often as a replacement for other elms killed by the disease, and there are now many mature trees. These appear to have been a godsend to the White-letter Hairstreak as the Sapporos provided habitat for the species when other elms were being decimated. Indeed, wherever there are Sapporos in South London there is the near certainty of a colony. However, it is not a long lived tree and is no longer being planted.
• Ulmus ‘New Horizon’ is a newer cultivar currently being planted in London and comes from the same cross as Ulmus ‘Sapporo Autumn Gold’. A colony of White-letter Hairstreaks was found in 2017 on the trees in Vauxhall Pleasure Gardens – which have been positively identified as New Horizon. This is significant because the butterfly has not been recorded breeding on this elm before.

Butterfly Conservation carries out trials of new disease resistant elm cultivars both to assess the quality of the trees and their use for breeding by the White-letter Hairstreak.

http://www.hantsiow-butterflies.org.uk/downloads/Disease%20resistant%20elm%20cultivars%20BC%20trials%206th%20report%202016.pdf

At present we cannot definitely say that New Horizon hosts the White-letter Hairstreak, which would require the finding of eggs. However it seems very likely that it does.

• Ulmus americana ‘Princetown’ is the other widely planted disease resistant cultivar in London. However it is not been found to be used by the butterfly and also may be susceptible to DED.   

Results

In VC17, the White-letter Hairstreak was first seen in 2017 on 12th June at Tooting Common and Nunhead Cemetery - about 10 days earlier than usual. The last sightings were on 26th July, about three weeks earlier than most years.

The butterfly was seen in many more locations in 2017 than previously. This is likely to be a result of the more intensive recording, rather than simply an increased abundance or distribution. However, it is clear that the butterfly is more widespread than previously thought.

In the boroughs of Wandsworth, Lambeth and Southwark the White-letter Hairstreak was seen at sites in Wandsworth Common, Putney Heath, Putney Lower Common, Clapham Common, Tooting Common, Battersea Park, Vauxhall, Streatham Common, Herne Hill, Nunhead, and Dulwich.

Records of the White-letter Hairstreak in VC17 for 2007-2017

Some of the sites are very urban in nature, especially to the north of the area (e.g. Vauxhall), showing that the butterfly can survive in apparently unwelcoming environments. Butterflies are associated in the public mind with rural settings but the White-letter Hairstreak appears to be equally at home in both the city and the countryside.

Vauxhall Pleasure Gardens – Ulmus ‘New Horizon’ with a colony of White-letter Hairstreaks, 23 June 2017

Results are shown in the table below. This is a subset of the database showing the locations where the butterfly was found in Wandsworth, Lambeth and Southwark in 2016 and 2017. There are however many more good locations in these boroughs that have yet to be searched.

All data has been submitted to iRecord (www.brc.ac.uk/irecord).

Acknowledgements

• Thanks are due to Bill Downey, Butterfly Conservation volunteer, for setting up and coordinating this project.
• This study would not have been possible without the hard work of countless volunteers - mostly members of Butterfly Conservation -  who assisted with verifying elm locations and looking for the adult butterflies.
• We appreciate the assistance of borough ecology officers, who provided details of elm locations from their databases:
• Valerie Selby, Principal Parks Officer, Wandsworth Council
• Kevin Freed, Contract Officer - Biodiversity, Wandsworth Council
• Jon Best, Ecology Officer, Southwark Council
• Iain Boulton, Borough Ecologist, Lambeth Council

Further reading

Butterfly Conservation information

• Website https://butterfly-conservation.org/679-709/white-letter-hairstreak.html
• Factsheet https://butterfly-conservation.org/files/white-letter-hairstreak-psf.pdf

Elms in Wandsworth, Lambeth and Southwark

Location	Tree	2016	2017	Grid Ref
Lambeth - Herne Hill - Brockwell Park	Ulmus New Horizon?		✓	TQ31218 74073
Lambeth - Streatham Common	U Sapporo Autumn Gold		✓	TQ30840 70928
Lambeth - Streatham Common	Hybrid Elm?	✓		TQ31099 71000
Lambeth - Streatham Common	Hybrid Elm?	✓		TQ31193 71020
Lambeth - Vauxhall Pleasure Gardens	Ulmus New Horizon		✓	TQ30519 78195
Southwark - Dulwich - Gallery Rd.	Huntingdon Elm?		✓	TQ33103 73769
Southwark - Dulwich - College Rd.	Huntingdon Elm?		✓	TQ33177 73376
Southwark - Dulwich - College Rd.	Huntingdon Elm?		✓	TQ33171 73319
Southwark - Dulwich Park	Wych Elm		✓	TQ33576 73296
Southwark - Dulwich - South Circular Rd.	Huntingdon Elm?		✓	TQ33004 73094
Southwark - Dulwich - South Circular Rd.	Hybrid Elm		✓	TQ33872 73321
Southwark - Dulwich - Lordship Lane	Wych Elm		✓	TQ34488 73276
Southwark - Nunhead Cemetery	?		✓	TQ3550 7565
Southwark - Nunhead Cemetery	?		✓	TQ3519 7553
Southwark - Nunhead Cemetery	?		✓	TQ3524 7547
Southwark - Nunhead Cemetery	?		✓	TQ3537 7546
Southwark - Nunhead Cemetery	?		✓	TQ3542 7544
Wandsworth - Battersea Park - SE corner	Wych Elm	✓		TQ28660 77110
Wandsworth - Clapham Common	Smooth-leaved Elm?		✓	TQ28745 74520
Wandsworth - Putney Heath	Smooth-leaved Elm?	✓		TQ23570 73748
Wandsworth - Putney Heath Wildcroft Rd	Smooth-leaved Elm?	✓	✓	TQ23375 73873
Wandsworth - Putney Heath - Telegraph pub car park	English Elm	✓		TQ23411 73653
Wandsworth - Putney Heath - Wildcroft Road	English Elm	✓		TQ23389 73901
Wandsworth - Putney Lower Common	Ulmus parvifolia?	✓	✓	TQ23129 76211
Wandsworth - Nine Elms Lane - Riverside Walk	Huntingdon Elms?		✓	TQ29804 77729
Wandsworth - Tooting Graveney Common	English Elm	✓	✓	TQ28777 71446
Wandsworth - Tooting Graveney Common	English Elm	✓		TQ28788 71445
Wandsworth - Tooting Graveney Common	Smooth-leaved Elm ?	✓	✓	TQ28876 71513
Wandsworth - Tooting Common	Smooth-leaved Elm ?	✓		TQ 28779 71450
Wandsworth - Wandsworth Common	Smooth-leaved Elm ?	✓		TQ 27295 73143
Wandsworth - Wandsworth Common	Smooth-leaved Elm ?	✓		TQ27359 73209
Wandsworth - Wandsworth Common	Smooth-leaved Elm ?	✓	✓	TQ27334 73290
Wandsworth - Wandsworth Common	Smooth-leaved Elm ?	✓		TQ2756073665
		16	22