Hertfordshire & Middlesex Branch

Distribution and Status

The White-letter Hairstreak is fairly widespread and common around elms in our branch area. During the 1970s Dutch Elm Disease had a devastating effect on elm which is the butterfly's larval foodplant but the butterfly can breed on regenerating young suckers at least until they reach a certain height. Disease-resistant elms are now being planted to ensure populations are maintained. Because of its elusive behaviour by mostly sitting around on the tree canopy, it is under-recorded so it is likely that more colonies are yet to be discovered. Mainly due to the research and efforts by Andrew Middleton and Liz Goodyear many new colonies were found in the two counties which is encouraging

Habitat Requirements

Hedgerows, edges of woodland and isolated clusters of elms even in urban areas. The same breeding sites tend to be used every year

Larval Foodplants

Wych Elm Ulmus glabra, English Elm Ulmus procera, [Ulmus minor agg. One disease-resistant form of elm is Dutch Elm also known as 'Sapporo Autumn Gold' Ulmus japonica]

Adult Food Sources

Bramble Rubus fruticosus agg., Creeping Thistle Cirsium arvense, Wild Privet Ligustrum vulgare. Honeydew

Behaviour/Observation notes

Like most of the other hairstreaks this species is not easy to find as it spends much of its time flitting over the tops of elm trees. Probably the best time of day to find it is in the early morning, say 09:00 hours, for males which actively defend their territories in the canopy. Any brown 'speck' jinxing about may well be a White-letter Hairstreak. Both sexes do occasionally descend to lower levels to feed on nectar but their wings are always closed when resting or feeding. The butterfly overwinters as an egg and searching for the eggs is a good way to find colonies. Finding flowery elms in the winter and early spring should be easy to locate with their pink or white blossoms

Life History

This species produces only one generation a year with adults emerging from the middle of June into July and the odd specimen lingering on into August. Females usually lay eggs singly, often on a scar between old and new growth or end-tips, and spends the winter in this stage. In the spring, larvae emerge to feed firstly on the buds then on the leaves. In June, a pupa is formed attached to a twig or stem