Side view of a butterfly with brown underwings which have a zig-zag white line and orange markings on the edge.

White-letter Hairstreak. Photo: David Tomlinson

A butterfly which has been hit hard by Dutch Elm Disease, as its caterpillars feed on elm. Its distribution in Dorset has been shrinking, but it is doing well at our Alners Gorse Butterfly Reserve, thanks (we hope) to the habitat being managed with the White-letter Hairstreak in mind.

Where to see

Habitat: It will be found near elm, but this could be anything from a mature tree (though they are rare) to younger growth in hedgerows.

Caterpillar foodplants: Elm species including Wych Elm, English Elm and Small -leaved Elm.

Best places: Our Alners Gorse butterfly reserve is the only publicly accessible place we can recommend, but also try Motcombe Meadows. It is worth watching the sightings pages of this website for odd sightings.

Reported from the following locations last year*:

When to see

June and July, possibly into August

Sightings by month (last 5 years)*:

Sightings this year*:


Notes

Size: small.

The loss of many mature elms to Dutch Elm disease was a fierce blow to this elm-dependant species. Though it was once thought to prefer mature elms, it is now often found on smaller growth, which may be a reaction to the loss of the bigger specimens. Young elms stay free of the disease until they reach 5-10 meters high, when their bark becomes suitable habitat for the beetles which spread it, and if this happens, they die. A lot of work has been happening nationally to find resistant strains of the elm.

A small butterfly. The male and female are similar, though the female is a little paler and may have longer tails. It always lands with its wings closed, so you will only get to examine its underwings in detail, though you may glimpse the upperwings in flight. The apparent colour of the underwings varies a lot with the light.

It is the darkest of our Hairstreaks, with brown underwings on which is a white line forming a W shape (though this is more pronounced on some specimens than others), and there are orange markings on the tail end of the hind wings. It has a small tail on the hindwings.

Your usual view, unless you are lucky, is of a “silver speck tumbling in the … sunshine and circling round a treetop” (quote from Dr Jeremy Thomas), but you may catch it coming down to nectar on bramble or thistle, though generally the adults live on aphid honeydew, found in the treetops.

Elsewhere, you might confuse this butterfly when it is on the wing with the Black Hairstreak, but this is not found in Dorset, so you can only confuse it with the more common Purple Hairstreak when flying; they look quite different when perched.

Photo gallery

Click thumbnails to view larger images.

*Please note: The charts shown on this page are drawn only from casual sightings submitted to this website. Records from this website will be added to a lot more data collected throughout the year and used to compile the five-yearly Butterfly Atlases for Dorset and the UK.