A typical Common Darter type for the site:
The taxonomy of Common and Highland Darter is comparable with that of Common and Scottish Crossbill - fraught with pitfalls and often vague ! However, the live specimens that I have examined in NE Scotland are markedly different from those more typical of nigrescens I found in Glen Affric and on the whole appear to be more characteristic of striolatum which seems to be spreading northwards along the east coast of Scotland. Last year I even had one in my garden in the city and there are no known pools in the neighbourhood. Most of the ID books I have do not show striolatum (Common) this far north but all my records will go towards the new Atlas.
Here is a profile of a basking striolatum from the site near Aberdeen :
Note the extensive black markings along the side of the thorax in nigrescens, the insect also appears more 'substantial' and robust though this may be age related. The black bands on segment 2 is not failsafe in my opinion as in the top picture these are thicker ala that suggested for nigrescens yet this specimen was clearly striolatum.
Here is one of my Glen Affric ones from July 2008:
A recent BDS Bulletin has a small update on research being conducted to determine whether or not nigrescens is a different species from striolatum. The preliminary results suggested no significant differences in DNA between specimens from Southern climes and those up here in the North, and that nigrescens is merely a 'dark morph'. Sounds familiar, ha-ha !