Thecla betulae
This is our largest hairstreak species, and Sussex is one of the best counties to see this beautiful butterfly. Although it is a reasonably common species, its reputation for being elusive is well founded, and it can be a challenge to find one. However, once an individual is located it rarely disappoints the keen photographer, especially if it busily feeding on a flowerhead. Whilst the adult butterflies may be difficult to find, their eggs are not, and in the winter of 2010/2011 there was a thorough search of the Sussex countryside, to map out the distribution of this species. On the Coastal Plain in West Sussex, there were just a few locations where eggs were found. Heading north, there were rather more on the South Downs, with greater numbers still on the Wealden Greensand. However, it was the Sussex Weald, which proved to be the county stronghold. In East Sussex, during “The Great Egg Hunt” there were relatively few eggs found east of the county town of Lewes.
The first adults usually emerge in the second half of July, with peak numbers recorded in the last week in August and the first week of September. When they first-emerge in July, the only confusion species might be White-letter Hairstreak, but these will be worn individuals, contrasting with the bright colours of a fresh Brown Hairstreak. It’s a very distinctive butterfly and identification should usually be straightforward. The flight period typically lasts the whole of September, with a few stragglers seen in October.
Quoting from the 2023 annual report: “There were some interesting new developments regarding Brown Hairstreak. They clearly had a very good season and the records over the past couple of years strongly suggest they are gradually expanding their range eastwards, further into East Sussex. There is good evidence of colonisation of the Polegate/Abbot’s Wood area and quite possibly the Eastbourne downland, as well. Unless these are isolated populations (possible, but unlikely) it follows that there are several small colonies in the area between Barcombe and Polegate, that have yet to be discovered”. There is no doubt that that this species is very gradually spreading eastwards from its West Sussex stronghold.
There are colonies all over West Sussex and especially in the Sussex Weald but finding a Brown Hairstreak for a close-up view, and then a photograph, is far from easy. The best location over the past twenty years or so has been the area known as the Steyning Downland Scheme. The woodland edge between TQ169112 and TQ166112 should be checked, as well as TQ166114 to TQ164113.
Male Brown Hairstreak at rest – photo by Martin Kalaher
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Male with open wings
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Female nectaring on Hemp Agrimony
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Male nectaring on Hemp Agrimony
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Female nectaring on Hemp Agrimony
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An aberrant photographed in 2019 (never previously seen as a wild specimen)
Butterfly Conservation Brown Hairstreak
