When I lived in Suffolk I saw the number of brown arguses increase dramatically from zero (I lived in East Suffolk) to its being a common heathland and coniferous woodland butterfly. I think it has generally expanded its range. Thus, it is something one should be increasingly aware of.
The ratio of male to female common blues changes through the season. The first blues on the wing are almost invariably males and they set up their territories for up to a week or so before females become very evident. There is then a period during which females become increasingly common, and finally they at least equal male numbers, in my experience. However, ancient males do seem to drag on and are often the last to be seen of a brood, perhaps because they don't have to expend so much energy on eggs and laying, and instead spend their days at the pub enjoying themselves.
Whenever my first sighting of a particular species of blue at a particular site is a female I suspect that she is a vagrant and that it is not (yet) a true breeding colony.
Re the underside brown argus/common blue distinction, a couple of things to note I didn't mention in my last post. Occasionally, common blues lack the cell spot (but brown arguses never have one). This form,
icarinus, is something I personally have only ever seen in males. Secondly, the 'colon' spots in
Aricia species may be quite oblique, but are always clearly out of line with the arc. I photographed this
artaxerxes (
allous) yesterday, after my post, and noticed that it had really very oblique spots - but they still show it is
Aricia.
Guy
