This time, I was expecting a new arrival as the collector had emailed me and given the background i.e. the habitat details and why the specimen was difficult to ID. It had been collected back in March 2010 on vegetation on a Lasius flavus anthill on a Derbyshire grassland. Initially it looked to be the common and widespread Chrysolina staphylaea, but a couple of features such as small size and heavy puncturation had induced the collector to look more closely and dissect it.
|The mystery Chrysolina...|
The lateral view above looks about right - there's a bit of clag on the tip, but the aedeagus is pointed right at the tip, then expanding so that there is a shallow dent near the tip on the inside of the curve. It's a bit obscured in the pic but it is there (honest). So, this is good for C. staphylaea. However, the dorso-ventral view is unusual and not the rounded shape expected. Leaving this aside for the moment, what about the other features?
Well, the size (a little over 6mm long) is fine for this species, although cited as 'smaller than others in my collection' by the collector but that's fine as there can be site/habitat/regional variations and so on. The punctures are a little coarse but again are within the normal range of variation, and the microsculpturing looks OK too. Also, though not diagnostic, the overall colour, habitat and so on are also fine for C. staphylaea. Now, the only other option (it certainly isn't any other known British species) would be a species new to Britain. Two were found so it isn't a single individual blown in from elsewhere, but could it be a newly-discovered British colonist? Well, it's possible, but looking through superficially similar species from continental Europe and the Mediterranean, nothing seems to have this combination of colour, size, habitat and aedeagus so it appears unlikely.
Therefore, after much musing, book/web-trawling and peering down microscopes, my conclusion is that it is an aberrant form of C. staphylaea - time (and the potential collection of more specimens) will tell whether the unusual aedegus is a constant feature and so whether it is something more important like a new subspecies... however, with any single apparently-aberrent specimen like this, it could be something else so I'll be looking again - and as ever, comments & suggestions are most welcome...