Sussex Butterfly Conservation : Species

Butterfly Species in Sussex

Male Brown Hairstreak at rest – photo by Martin Kalaher

Brown Hairstreak

Thecla betulae

Description

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 and 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 dark brown uppersides of the female contrast with the large panels of dusky orange on the forewings. There is also a small amount of orange surrounding the long, graceful hindwing tails. The undersides are a mix of different shades of ochre and on the hindwing, there are one-and-a-half white hairstreaks, running parallel to each other. A fresh specimen is a stunning insect. The male has much smaller dusky orange patches on the upperside forewings, and the colours of the undersides are rather subdued, compared to the female. When these butterflies 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. The other obvious difference is that Brown Hairstreaks open their wings to sunbathe, whilst White-letter Hairstreaks habitually close their wings, when perched.

Between 2006-2024 an “average first sighting” was July 23rd (range, July 2nd to August 5th). Some outstanding lepidopterists monitor the Brown Hairstreak population on the Knepp Estate and an analysis of their records since 2017 brings forward the “first sighting date” to July 14th. Peak numbers are recorded in the last week of August and the first week of September. The “average last sighting” for 2006-2024 was October 1st (range, September 9th to October 20th).

Eggs are mostly laid on Blackthorn, but Wild Plum, Cherry Plum, and occasionally even Victoria Plum.

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.

Where to find

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.