Last year I was sent these two photos of an interesting Brown Argus Aricia agestis by Tim Alps. Tim has a keen interest in encouraging wildlife into his large butterfly friendly garden in Aldbury where I have been working regularly for a few years. The photos were taken last May on the limestone grassland above Whipsnade Zoo, an excellent site for Downland butterflies. The specimen clearly shows that the black discoidal spot on the upper forewing is partly ringed with white. I have not found any reference to this feature in any of my books, but I have come across the odd photo of similarly marked butterflies on the internet. These butterflies appear to have similar markings to a small proportion of the salmacis subspecies of Northern Brown Argus Aricia artaxerxes, sometimes known as the Castle Eden Argus, which is only found in Northern England. The majority of specimens belonging to salmacis, have a black discoidal spot, but a small percentage have a white spot and resemble the Scottish subssp artaxerxes. Less than 10% of specimens have a small black discoidal spot faintly ringed with white, somewhat similar to the Brown Argus pictured below.
For many years Northern Brown Argus was considered to be a subspecies of Brown Argus but was eventually classified as a species in it's own right. Studies have shown that some of the colonies along the border of the two species ranges have been incorrectly classified and some colonies in the north of England are now considered to be A. agestis. Although the range of the two species does not overlap that situation may change as Brown Argus expands northwards as a result of global warming.
Brown Argus Aricia agestis, Whipsnade 26/05/2010 - (Tim Alps)
Brown Argus Aricia agestis, Whipsnade 26/05/2010 - (Tim Alps)
I'm fairly sure that the oddly marked Brown Argus on the right is a female due to the bold orange markings that reach the wing tips, and that the left-hand butterfly is a male as the sparser markings taper off and fade away. The male should be smaller than the female, with less rounded wings, but this specimen gives the impression of being noticeably larger, which is rather confusing. Strangely enough whilst searching through my own photos I came across a dreadful shot that I took several years ago at Whipsnade of a similarly marked Brown Argus, making me wonder if this aberration is present in some colonies but absent from others.
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