A White-letter Hairstreak at Ryton Wood. © 2007 - 2021 Steven Cheshire.
The White-letter Hairstreak is a small, brown butterfly which has an erratic flight. It is difficult to spot, even when searching for this species at a known colony which makes it a difficult species to monitor because it spends most of its time high in the tree canopy feeding on honeydew deposits produced by aphids. They do occasionally feed on flowers that produce good quantities of nectar such as Wild Privet (Ligustrum vulgare), Common Ragwort (Jacobaea vulgaris) and Creeping Thistle (Cirsium arvense), especially after periods of rain which reduces the availability of honeydew. The butterfly always settles with its wings closed.
The species is widespread in Warwickshire but occurs in very low numbers. Most observers are lucky to see more than one or two individuals in a season.
The White-letter Hairstreak prefers sheltered hedgerows and woodland rides where Elms (Ulmus spp.) grow. TThe butterfly has been severely affected by the impact of Dutch Elm Disease on its larval foodplant since the 1970's which killed the vast majority of our mature Elm trees in the UK. Small colonies of the White-letter Hairstreak rely on one or two suckering Elm trees for their survival, so the loss of a single Elm can result in the extinction of a colony.
Unfortunately, our Elm trees continue to disappear. This is not only caused by the continued presence of Dutch Elm Disease. In 2011, a newly discovered breeding colony (first confirmed in 2009) supported by just two suckering Elm trees was lost due to railway line enhancements near Weddington, Nuneaton. The butterfly has not been recorded in this area since.
The primary larval foodplant is English Elm (Ulmus minor). Wych Elm (Ulmus glabra) is also used as are many Elms Ulmus sp.
Single Elm tree can able to support a colony of the White-letter Hairstreak butterfly. By planting English Elm (Ulmus minor) in your garden, you are sure to attract this butterfly once the tree matures. You can also opt for the European or White Elm (Ulmus laevis) or a more ornamental species such as the disease-resistant 'Sapporo Autumn Gold' (Ulmus japonica).
The White-letter Hairstreak can be found throughout Warwickshire wherever Elms (Ulmus spp.) occur.