www.ukbutterflies.co.uk

These pictures show a leafy country lane, with ancient hedgerows on both sides consisting almost entirely of vigorous elm. This is part of a network of lanes covering many miles, with thousands of elms forming a dense hedgerow. There are good numbers of mature non-elm trees like oak, ash, beech and sycamore. There were also huge elms historically, now gone. There is lots of caterpillar feeding damage on these hedges, per the picture.

The question is: Is this suitable White-letter hairstreak habitat? Initially I thought these annually cut hedges would be a disaster for any WLH, as they might attract egg-laying but the eggs would be destroyed in the cutting. However I remembered that WLH lay eggs on the join between old and new growth, so if the hedge is not cut back any harder than the previous year, they would survive. In fact could this behaviour even be in response to hedge cutting? You can see how natural selection would quickly favour butterflies that did this over these that laid eggs on new growth.

These hedges will be non-flowering, but they are very vigorous presumably because they have ancient root systems but little above ground, so all the energy from the roots can produce very long (approx 2m), large-leaved shoots each year. I know that WLH early instar larvae eat flower buds, but also I have read (in Peter Eeles' Lifecycles book) that they can use non-flowering shoots, which come into leaf early.

For context, I am researching survey sites for next year in an area of Scotland where WLH has only recently been reported. Nobody has looked for WLH in this habitat yet. I will of course try to look for myself next year and find out one way or another, but I was just wondering how good a target this habitat would seem to be for searches, based on any experiences of hedgerow habitats within the currently known WLH distribution.

There are similar lanes here in Essex, one along Cherry Tree Lane at Friday Woods near Colchester, and the other at Langdon Hills Country Park near Basildon where I have found WLH who seem to be thriving in the site conditions including aspect, topography, and shelter. Plus I don't think the colonies are isolated which obviously helps. That is despite the on-going damage caused by Dutch Elm Disease.

Here in east Somerset there are many lanes like this. I don't think I've ever seen the butterfly or found the early stages except where small groups of elms have got away from the flailers and grown to a bigger height - at this point they are quite likely to get colonised by the butterfly (and also the rare but under-recorded Lesser-spotted Pinion moth, which also seems to like these kind of sites).

Thanks for the info, both. Looking forward to searching next year.

Chris

In their 1986 Butterflies of Suffolk, Mendel and Piotrowski note that the largest colony of white-letter hairstreaks in the county (at that time) was supported by 'an elm hedgerow just outside the Borough of Ipswich'. The colony is referred to again in the Millennium Atlas of Suffolk Butterflies, though by then the area had been cleared for housing and the hedgerows were in dispute. I wonder if a response to Dutch elm disease was a shift towards a greater use of young, non-flowering elm.

Guy

Thanks Guy, interesting to know. I will aim to report what I discover about habitat preferences on the north edge of the range.