The Northern Brown Argus is as its name suggests is a northern species which is found in the Northern end of Britain.  It is found in scattered colonies as far south as Cumbria and Durham.  It is found in small colonies across Northern England and Scotland where the numbers are generally less than 200 butterflies in a colony.

It is very similar in appearance to the Brown Argus, and the geographical North to South split is one of the best ways of telling these two species apart.  They are similar in appearance to the female Common Blue as well as the Brown Argus and without the geographic split it would be hard to tell these butterflies apart other than for a few differences in the white spots on their wings.  There are also differences in the eggs, caterpillars, and Chrysalis.  There are also regional variations between the Brown Argus and there are several subspecies which include Scottish and Castle Eden, but again these are generally driven by geographic boundaries.

I have seen these butterflies in both Scotland and Northern England, the images below were taken on a trip to a Small Blue colony in County Durham.