Male, Switzerland, September 2017
Aricia artaxerxes
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Male, Switzerland, October 2014
Male, Switzerland, June 2018
Male, Switzerland, July 2019
Male, Switzerland, August 2014
Male, Switzerland, June 2012
Male, Switzerland, July 2012
Male, Switzerland, October 2017
Male, Switzerland, June 2011
Male, left, with a female common blue, Switzerland, November 2013
Male, Switzerland, June 2012
Switzerland, May 2007
Switzerland, May 2007
Switzerland, May 2007
Distribution
The name 'northern brown argus' refers to this butterfly's distribution
in the UK, where it is found only in Scotland and in the north of
England. The Scottish subspecies, Aricia
artaxerxes artaxerxes, which I have never seen, is
distinguished by having a white discoidal spot on each forewing. The
English subspecies, salmacis,
lacks this spot, as does the continental subspecies, allous. What were
once considered the Pyrenean and Spanish races of this butterfly are
now treated as a distinct species, Aricia montensis.
All the photographs above show males of the subspecies allous - I don't seem to have any pictures of females. The butterfly is similar to the brown argus but has noticeably more pointy wings, especially in the male, and greatly diminished orange markings on the forewings. Like the brown argus, the northern brown argus may be distinguished from brown female blues by the complete absence of any blue scales on the wings. Also like that species, the two uppermost spots in the postdiscal sequence on the underside hindwing are slightly separate from the others, forming a colon. There is no cell spot on the underside forewing.The white fringes of the wings are half-chequered - this may be quite conspicuous.
The northern brown argus is a montane species, though in
Switzerland
it flies as low down as the Rhône Valley, at 500m. Generally, it
replaces the brown argus at altitude and in the north of Europe but
there are large regions of altitudinal and geographical overlap. The
books describe it as single-brooded, flying from June to August or
September, and this is true in the mountains in Switzerland. However,
it is on the wing into October or even November in the valley and I
have always assumed it to be double brooded or more there. The
foodplants are various plants in the geranium family, including
cranesbills, rock-roses and storksbills. It hibernates as a caterpillar.