Scotch Argus butterflies at Smardale Gill NNR, Cumbria but not Arnside Knott – 25th Aug

This bank holiday weekend offered a suitably fine weather window to experience one of the three remaining British butterflies I had not observed previously. Having been on stand-by all through August after Ewan declared his intention to make the long drive north if conditions were right, the go ahead now came. So after a 3am start at home I met him at his house in west Oxfordshire two hours later and off we set.

Scotch Argus (pictured below) occurs at just two sites in England, both of them in Cumbria, but is much more common further north where it is known as the “Scottish Meadow Brown”. This is one of the last butterflies to emerge in late July each year, flying throughout August though rarely into September, and so usually requires a separate trip from other northern specialities to encounter. The issue as always with insects if a wasted journey is to be avoided is sufficient sunshine for them to be active, and this butterfly is a true sun lover.

We arrived at the second site, Smardale Gill NNR (NY740083) in the late morning. This very beautiful reserve in the upper Eden valley, administered by Cumbria Wildlife Trust (see here) follows the course of a former railway line for a mile and a half (2.6 km) along a steep hillside of ancient woodland above the intriguingly named Scandal Beck. After a while the track-side habitat becomes very wild flower rich with masses of Knapweed and Scabious that simply teemed with butterflies, mostly late summer, second brood Vanessids.

In amongst that colourful array – Red Admiral, Painted Lady, Comma and especially huge numbers of Peacock Butterfly – were the smaller, brown item of our quest that were most numerous in one hot spot around 100 metres in length. The first one we located (below) prompted a celebratory high five but it soon became apparent there were many more here. We estimated there were over 100 Scotch Argus flying today. Females of the species are known to be sedentary, not venturing further than such a distance, which could explain this concentration we came across.

Being well into their flight season a lot of the butterflies we observed today were quite faded and / or worn, but amongst all these some fresher individuals stood out. They are roughly the size of a Ringlet but with a rather weak, jerky rolling flight and a tendency to settle low down in long grass. When nectaring on flower heads they stayed constantly on the move, and so were not easy to take acceptable pictures of. This was the first serious work out for a used Nikkor telephoto lens with which I recently had to replace my as obsolete previous one, and the results are OK given the bright and glarey conditions.

Earlier in their adult life cycle Scotch Argus are a much richer chocolate brown, and like Ringlet can appear almost black when most fresh. The dusky upper wings exhibit rust brown patches adorned with black spots with intense white centres. Hence the common name of “Argus” after a giant in Greek mythology that possessed 100 eyes (per Thomas and Lewington). The under-wing ground colour is grey and deep brown, with a prominent paler band similar to that seen in Meadow Brown.

The food plant for the Cumbrian colonies is Blue Moor Grass that dominates the scrubby limestone sites these butterflies occupy. The widespread Scottish populations, that replace the Meadow Brown in higher areas, utilise a variety of habitats including damp grassland, bogs and woodland edges where the larvae feed on Purple Moor Grass. These are usually the commonest butterfly of late summer where they occur.

For an insect that inhabits some of Britain’s wettest regions, seeing Scotch Argus is dependent extraordinarily on sunlight, since they vanish deep into long grass cover as soon as any cloud appears to as quickly re-emerge in numbers when the sun comes out again. Males fly much more than females in an endless search for mates, and it was noticeable today how they would challenge and chase off the many, much larger Peacocks at this site.

Smardale Nature Reserve follows the course of the former South Durham & Lancashire Union Railway that from 1861 to 1962 transported coke for the iron and steel industry across the Pennines from Darlington to the West Cumberland area. This section is crossed overhead by the Smardale Viaduct, one of 17 along the 72-mile Settle to Carlisle main line, one of northern England’s most scenic railway routes. Further along the reserve path the as magnificent structure of the Smardale Gill Viaduct is reached, a truly uplifting, even awe inspiring location.

smardale gill viaduct.1901

Smardale Gill Viaduct

Since 1990 this impressive and dramatic structure, 30 metres high on 14 stone arches, has been owned and maintained by the most excellent Northern Viaduct Trust (see here). The story of this and more nearby industrial railway relics’ rescue from demolition, and funded restoration to become public recreational amenities, is to say the least heart warming. Walking guides to the entire complex can be downloaded from the above link.

The track bed across the viaduct’s top is nominally closed due to “safety concerns” over the very robust looking hand rails, but there is nothing to prevent walkers from continuing. Notices on the valley side further warn of “danger from falling masonry”, of which there seemed little risk. But I suppose someone is always likely to hurt themselves and then wish to sue the so well intentioned owner. We found a second cluster of Scotch Argus activity on these grassy slopes (pictured above).

smardale gill viaduct.1904

Me at Smardale Gill Viaduct

Our day in Cumbria had begun at 9:30 am with a visit to the other, coastal site Arnside Knott (SD455775). We searched the top of this hill that is said to be best for Scotch Argus in August, but the uneasy feeling from when we had failed to find High Brown Fritillary here in July 2018 quickly set in. Ewan had subsequently seen three Scotch Argus at this place on a brief visit of his own while driving south from Scotland a year ago. But today we found almost nothing of any note, except for one faded Northern Brown Argus and a Wall Brown.

This location is still cited as a classic one for both HBF and SA. But earlier this year a regular visitor I met in the field affirmed the former are now in decline there. A recent scientific paper (see here) corroborates that despite managed re-colonisation between 2004 and 2016, overall abundance of HBF in the Morecambe Bay area continued to decline with further extinctions, due in part to less host plant (Violet) for caterpillars to feed upon in a cooler micro-climate.

Today a volunteer at Smardale Gill said 2019 has been a very poor year for Scotch Argus too at the first site. There must be habitat management reasons why numbers of both former specialities have fallen so much, and the evidence is that Arnside Knott is no longer worth bothering with. By contrast our visit to Smardale Gill NNR was simply superb.

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