*Brown Hairstreak | Thecla betulae (female), Arnside & Silverdale AONB (Mike Watson)*

LAST OF THE SUMMER BUTTERFLIES. The last two single brood butterfly species to emerge are usually Scotch Argus Erebia aethiops and Brown Hairstreak Thecla betulae. The former is easy enough to see, particularly at its mega colony of Smardale Gill, but Brown Hairstreak is not nearly so. It was re-introduced to the Morecambe Bay limestone in, or prior to, 2011 having gone extinct in the Arnside/Silverdale area in the 1930s. This was a private release and I have no idea if it has been supplemented since but it can now be seen with some regularity at several spots here. Just like in its southern haunts, it is particularly fond of Hemp Agrimony nectar, where it can be ridiculously tame.

Scotch Argus Erebia aethiops had already been on the wing for a couple of weeks at Smardale Gill ,where, unlike the suggestions online, it is not in the floral verges of the disused railway line, rather on the steep unimproved alkaline grassland opposite the viaduct itself. It was abundant, I saw around 50 walking across the grassy slope but many were quite worn. It is a 2.5km walk each way from Smardale Hall and I will remember that the northwest facing slope is in shade until late morning. There was not much else here though, just a few tatty Meadow Browns Maniola jurtina and Gatekeepers Pyronia tithonus.

The impressive viaduct has 14 arches and carried the South Durham and Lancashire Union Railway for 101 years until the line’s closure in 1962, one year before the Beeching Report. The trains that crossed it transported coal to the steelworks in Barrow but when they closed there was no longer any need for this route.