Brown Hairstreak

Scientific Name - Thecla betulae

Flight Period - July to October

Overwinters as - Egg

Habitat - Hedgerows, Woodlands

Larval foodplants - Blackthorn

Conservation status - BC Priority High

Northamptonshire distribution - Very localised, limited to one area in the south of the county

Best public sites to see them - The footpaths around RAF Croughton

A Brown Hairstreak egg south of RAF Croughton

The Brown Hairstreak has been absent from Northamptonshire for half a century. However, the species has been steadily increasing its range in neighbouring counties, and in recent years eggs were found tantalisingly close to our county border with Oxfordshire. Then on the 20th of December 2023, Brian Laney (joint plant recorder for Northamptonshire) struck gold when he found a Brown Hairstreak egg on a Blackthorn south of RAF Croughton. A subsequent search found another four eggs in the area and a few weeks later another egg was discovered to the north of the airbase in Croughton Quarry. There is a lot of young Blackthorns along the A43 so it is highly likely that the species have used this corridor as a way of getting into the county. The eggs south of RAF Croughton were all found along a public footpath that runs along the southern and western boundaries of RAF Croughton (see map below) so this would be the best area to look for adults in late summer. The area can be easily accessed via a large lay-by on the A43 but please be aware that RAF Croughton is an active military base and abide by any signs that maybe in place. Please also note that the eggs are often far easier to find than the adults but please let me know if you record any.

Brown Hairstreak Distribution 2023

Brown Hairstreak (photo taken at RSPB Otmoor)

Brown Hairstreak (photo taken at Butterfly Conservation’s Ryton Meadows)

Brown Hairstreak egg locations south of RAF Croughton