I emerged from hibernation a few weeks ago and visited my own personal small Nature Reserve purchased thirty years ago and managed with wildlife and plants in mind ever since.
On arrival delighted to flush a couple Hares who quickly legged it away and soon out of sight. When I first got it, it was mainly grassland with some mature Oaks and Elms in the hedgerow borders. Then I saw Hairstreaks high over the Elms and Oaks but never got near enough to identify White Letter Hairstreaks. The Puprlpe Hairstreaks were much more cooperative and frequnetly come down to ground level and are easily identified. Back then, I had not realised a single lone Oak could support a colony of Purple Hairstreaks. I thought it was a butterfly of the larger woods and forests. As a schoolboy in the 1950s, I was able to find the early stages of the White Letter Hairstreaks in many parts of Gloucestershire and they did indeed live on single larger Wych Elms even in the middle of a large field. Sadly all such Elms long since gone. Now I know Purple Hairstreaks do that..
Over the years the range of wildlife seen in my "reserve" has been a delight to observe. Probably the best single observation being a GosHawk plunging into a dense Wild Rose and Blackthorn ( Sloe ) thicket just before dark in the late summer evening to reveal an explosion of small roosting birds and the |Hawk emerging at speed chasing one it had singled out. Amazing sight.
Anyway back on track. There is a range of Butterfly species there still although the grassland is much overgrown. Last winter, I employed and agricultural contractor to bulldoze the masses of thorny Scrub which had covered more than half the grassy area. This winter, with those bulldozed shrubs fully dried out, I set about burning them. Boy did they burn! That's better. The grassland species should benefit and recover with a larger area of grassland available. Nature can repair quickly if allowed to do so. Over the years, I have easily found Purple Hairstreak Ova ( eggs ) tucked into the winter leaf buds where they will hatch in the warmer spring temperatures. Despite frequent searches of the Oaks' winter buds there, I have yet to locate a single Purple Hairstreak Ovum on any of the Oaks in my field. That changed this late winter when I found them even low down on buds at eye level. Glad about that.
Some of my Elm "Suckers" are approaching maturity and could support White Letter Hairstreaks if there are any about still locally. I have seen them flying and found their eggs relatively easily in other parts of the county. I hope to see a return. I have even seen a female White Letter in the City Centre of Gloucester and this and other evidence indicates that they do move about possibly in search of better habitats to populate. Most butterflies do this as I have observed many species well removed from their usual habitat intent on seeking pasture anew.. Good for them.
Those Blackthorn thickets are large enough to support Brown and Black Hairstreaks but despite always on the look out, never seen one there. According to one butterfly breeder I've known for years, both those Blackthorn species are easy to introduce to suitable habitat. Very tempting. By the way, when searching Blackthorns elsewhere in winter for ova of the two Hairstreaks known to use this foodplant, I also found the unmistakable ovum of the White-Letter ... on Blackthorn. From that single ovum I raised a fine female specimen whose larva fed up on the white flowers initially and then moved to the leaves when they appeared. Closely related species not found in the UK on the European Mainland also feed on Blackthorn.
So, there are a few other Butterflies which feed on the Trees as larvae. These include Comma, Brimstones and the Purple Emperor. I have found the early stages of the latter species on Salix ( Broad leaved Sallows ) on Sallow Trees as large as any Forest Oaks in an Hampshire wood. Woodland maintenance usually means Sallows are cut down before they can reach that level of maturity. The number of Moth species larvae which feed on the trees of the forest is in the hundreds. Often Butterfly Tree foodplants are not allowed to reach mature tree status due to woodland management practices.
With the above in mind, if you know where to look, it is possible to see Purple Emperors in the UK on any day of the year. Try some winter searches. When you get your "eye in" you'll be surprised what you can find if you are patient.