Satyrium w-album, White-letter hairstreak

White Letter Hairstreak

Satyrium w-album

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Female, Switzerland, July 2018

Satyrium w-album

Female, Switzerland, July 2017

Satyrium w-album

Male, Switzerland, July 2016

Satyrium w-album

Female, Switzerland, July 2013

Satyrium w-album

Female creeping around a dense elm tree looking for places to lay, Switzerland, July 2017

Satyrium w-album

Female, Switzerland, July 2013

Satyrium w-album

Female, Switzerland, July 2012

Satyrium w-album

Male, Switzerland, July 2012

Satyrium w-album

Male, Switzerland, July 2012

Switzerland, July 2009

Switzerland, August 2008

Satyrium w-album ova

Eggs, resembling miniature UFOs, on wych hazel, Switzerland, October 2017

Satyrium w-album egg

Eggs, October 2017

Satyrium w-album larva

First instar caterpillar, freshly emerged from egg, Suffolk, UK, February 2021

Satyrium w-album larva

Second instar larva on unfurling elm leaves, Suffolk, UK, May 2021

Second instar larva on unfurling elm leaves, Suffolk, UK, May 2021

Satyrium w-album caterpillar

Third instar caterpillar, Switzerland, May 2017

Satyrium w-album caterpillar

Freshly moulted third instar caterpillar, with its old skin, Suffolk, UK, April 2020

Perfect camouflage! Suffolk, UK, April 2020

Larva beneath wych elm leaf, Switzerland, May 2010

The same larva

Two caterpillars beneath elm leaves, May 2016

Larva beneath wych elm leaf, Switzerland, May 2010

The same larva.

Satyrium w-album larva

Larva prior to pupation, after turning brown, Switzerland, May 2014

A caterpillar preparing to pupate, Switzerland, June 2010

Satyrim w-album pupa

Pupa, Switzerland, June 2010

Satyrium w-album pupa

A pupa, June 2014

Spain, July 2005

In the UK I nearly always see white letter hairstreaks on bramble but in the Val d'Aran they were particularly attracted to flat, white flower clusters like these.

Spain, July 2005

Distribution

In much of Europe, this is the commonest Satyrium hairstreak. I have seen it almost everywhere I've been, from the Pyrenees to the Oslo Fjiord and from the west of England to Hungary. It does not fly in most of Iberia, though, where many other species of Satyrium do fly. Despite its relative abundance and wide distribution, it is rather elusive and much less often seen than other equally common species. For much of the day, males keep to the canopy, where they can be spotted with binoculars if you know where to look but are otherwise invisible to the casual watcher. Mated females spend hours and hours creeping around in elm trees looking for perfect places to lay their eggs. Both sexes readily come to nectar but often at rather particular times of day in particular places. For these reasons, this is probably an under-recorded butterfly.

Most individuals are readily identified by the strong W shape in the hairstreak near the anal angle of the hindwing. When this is not obvious, the orange submarginal lunules are diagnostic, being contiguous and forming something like a zigzag orange band. All in all, this is a very distinctive species. Males can be distinguished from females by the shorter tails and the imprint of the sex brand on the underside of the forewing, near the end of the cell.

Eggs are laid in July near flower buds of elm. Near me in Switzerland, wych elm is preferentially chosen. The eggs hatch in April when the elm flowers burst and the caterpillars initially feed in these. Later, in May and June, they move to the leaves, where they leave a characteristic feeding pattern. They are a strange, jagged slipper shape - quite unmistakable. At some stage in June they move to a tailored leaf and change colour and shape to become a 'pre-pupa'. This then sheds its furry skin and becomes the leathery, slightly bristly pupa. The butterflies typically emerge at the beginning of July and fly through until August. Towards the end of their lives they spend more and more time nectaring and become easier to see.