Steven Cheshire's British Butterflies
British Butterflies: Species: Species Account - The White-letter Hairstreak:
White-letter Hairstreak
Satyrium w-album (Knoch, 1782)

White-letter Hairstreak egg.
  White-letter Hairstreak caterpillar.
  White-letter Hairstreak chrysalis
White-letter Hairstreak
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Insecta: Lepidoptera : Family Lycaenidae: Subfamily Lycaeninae : Genus Satyrium: Species w-album:

The White-letter Hairstreak is a small chocolate brown butterfly. The upper sides of their wings are only ever seen in flight as the butterfly always settles with its wings closed.

In the sub-marginal area of the underside of the hind wing is a narrow jagged black line with a wider band of deep orange extending towards the marginal area and small metallic blue spot or lunes in fields S2 and S3. Freshly emerged individuals also have a short tail to the wings at V2 but this is often absent in older individuals. The most distinctive feature is as its common name suggests a white line in the form of a 'w' on the underside of the hind wings. One arm of this 'w' extends onto the discal/post discal area on the underside of the forewings.

The Black Hairstreak is similar in appearance and size and both species may be encountered together in some locations as their flight period and habitats do overlap. However, the Black Hairstreak has a clearly defined row of black spots along the sub-marginal area of the underside of the hind wing.

Its erratic flight and its tendency to spend the majority of its time high up in canopy feeding on honeydew produced by aphids makes it a difficult species to see. On rare occasions it can be found feeding on the flowers of Creeping Thistle, Ragwort or Bramble blossom, usually after a period of rain which has washed leaves in the tree canopy clean of honeydew. Where it does occur, is rarely seen in double figures.

The female White-letter Hairstreak lays her eggs on mature Elm trees or abundant Elm sucker growth. The egg is dark green when first laid but quickly turns dark brown with a white rim and is a slightly domed disk in shape. The eggs are usually laid singularly on the girdle scar of a bud. The best place to search for eggs is near the end of the branch on the sunniest side of the tree. The eggs overwinter and are easily found when the trees have lost their leaves.

The larvae have a black head with a yellow-green body. They first feed on the blossom, developing buds and young shoots of Elm from April. The larvae are difficult to find during their final instar in May as they resemble a folded Elm leaf and are extremely well camouflaged.

The pupa usually forms during late May into early June and is most commonly found attached to a leaf or twig on the larval foodplant.  It has one brood per year flying from the beginning of July to mid August although butterflies may emerge earlier in some years following a warm spring.

The survival of the White-letter Hairstreak depends upon Elm trees. This species declined dramatically in the 1970's when its larval foodplant was and still is affected by Dutch Elm disease.

Up until 1906, the White-letter Hairstreak had been given four scientific names and at least six common names including 'The Hairstreak', 'Dark Hairstreak', 'W-Hairstreak', White-W Hairstreak', and most confusingly the 'Black Hairstreak' which is a completely different species. As a result, there is some confusion in the early literature as to what species the authors were actually discussing. It was Kirby in 1896 who gave it the common name we use today (Davies, M. 1992).

The type specimen of the White-letter Hairstreak held at the Natural History Museum in London has a small orange anal spot on the upper side of the hind wings but interestingly, in the UK, the butterfly lacks this spot as a result are almost all of the form

White-letter Hairstreak Survey
A new national survey for the White-letter Hairstreak began in 2007. Further information can be found at
The White-letter Hairstreak Recording Project web site.

The White-letter Hairstreak is a Priority Species for conservation due to the continued loss of habitat and resulting drop in population.

Sheltered hedgerows and woodland rides where Elms grow.
Throughout England no further north than Newcastle. Also occurs in parts of Wales.

Dutch Elm Disease is thought to be one of the main factors in the drop in numbers of the White-Letter Hairstreak although the true distribution of this species may not be fully known due to its secretive behaviour.
Where to see the White-letter Hairstreak in the British Isles
Other notes
Dutch Elm Disease:
Dutch Elm Disease is a type of fungus called Ophiostoma ulmi which is spread by bark beetles (Scolytus scolytus and Scolytus multistriatus) and was first recorded in the UK in 1927 at a site in Hertfordshire.

This was a less aggressive strain than that which reached our shores in the late 1960's. By 1977 over 50% of English Elm's had been killed by this new strain of the disease. The beetles which spread the disease feed high up in the tree. Exposed tissue e.g. cracks in the trees bark allow fungal spores spread by the beetles to enter the tree. The disease spreads rapidly on English Elm's but Wych Elm appears to be tolerant of the disease and it is known that the White-Letter Hairstreak can breed on Wych Elm.

The three recognised species of Elm present in the UK can be distinguished in the following way:

1. Wych Elm - Leaves are hairy on top large (greater than 7cm long) with a short stalk (less than 3mm).
2. Smooth-Leaved Elm - Leaves smaller (less than 7cm) smooth above longer than they are wide, hairless stalk/shoot.
3. English Elm - Leaves small, rough on top, nearly circular with very asymmetric base, hairy stalk/shoot.
Lifecycle chart
Flight chart
The lifecycle and flight charts should be regarded as approximate guides to the White-letter Hairstreak in Britain. Specific lifecycle states, adult emergence and peak flight times vary from year to year due to variations in weather conditions.
IUCN category status 2010 5   IUCN category status 2007 34
Endangered Endangered

5Fox, R., Warren, M., Brereton, T. M., Roy, D. B. & Robinson, A.
(2010) A new Red List of British Butterflies. Insect Conservation and Diversity.
Endangered Endangered

3Fox, R., Warren, M & Brereton, T.
(2007) New Red List of British Butterflies. Butterfly Conservation, Wareham.

4More information about IUCN categories.
UK status
Larval foodplants
Wych Elm (Ulmus glabra), English Elm (Ulmus procera) and Small-leaved Elm (Ulmus minor). Research has suggested a higher breeding rate on Wych Elm. It has also been shown that the larvae can survive on the Dutch Elm Disease-resistant variety Sapporo Autumn Gold (Ulmus japonica).

The White-letter Hairstreak population and distribution has been seriously affected by Dutch Elm Disease on its larval food plant in the UK. The major declines in Elm and subsequently the White-letter Hairstreak occurred during the 1970's and 1980's.

Butterflies of Britain ID Chart
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Butterflies of Britain (Laminated ID Chart).
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Population trends 1
UK Population trend 1995-2004 down by -63%
UK Population trend 1976-2004 down by -71%

1Fox, R., Asher. J., Brereton. T., Roy, D & Warren, M. (2006) The State of Butterflies in Britain & Ireland, Pices, Oxford.
UK BAP status 2
UK BAP status candidate priority species (link)

2For information about the UK Biodiversity Action Plan, visit the JNCC web site

National Biodiversity Network Gateway
National Biodiversity Network Gateway Distribution Map

Areas in and indicate a contraction in distribution of the White-letter Hairstreak except in Ireland where data is only available up until 1999.

* Records shown in outside the natural distribution may be the result of illegal or accidental releases by breeders or, depending upon the species, migrant individuals from mainland Europe.

Key to map*
= 2000 to 2010 inclusive (current distribution)
= records from 1950 to 1999 inclusive
= records from 1900 to 1949 inclusive
Records prior to 1st January 1900 are not shown.

The NBN Gateway records are shown on the map right. (See terms and conditions).

More data is available on the White-letter Hairstreak on the NBN Gateway web site.
Powered by NBN Gateway.
For full details of books and reports mentioned on this web site, view the references page.

Find out more online*
White-letter Hairstreak can be found on Peter Eeles excellent UK Butterflies web site.
White-letter Hairstreak can be found on Matt Rowlings excellent European Butterflies web site.

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Photographs of the White-letter Hairstreak
Image ID BB923 - White-letter Hairstreak - © Steven Cheshire
White-letter Hairstreak unknown (imago)
BB923 ©
Image ID BB922 - White-letter Hairstreak - © Steven Cheshire
White-letter Hairstreak unknown (imago)
BB922 ©
Image ID BB208 - White-letter Hairstreak - © Steven Cheshire
White-letter Hairstreak unknown (imago)
BB208 ©
Image ID BB207 - White-letter Hairstreak - © Steven Cheshire
White-letter Hairstreak unknown (imago)
BB207 ©
Image ID BB86 - White-letter Hairstreak - © Steven Cheshire
White-letter Hairstreak unknown (imago)
BB86 ©
There are 5 photographs of the White-letter Hairstreak in our stock photo library.
Aberrations and forms
There are 3 named aberrant forms of the White-letter Hairstreak currently listed. Find out more about aberrants here.

ab. albinotica - Goodson  1959
ab. albovirgata - Tutt  1907
ab. rufextensa - Goodson  1959