Time after Time, us amateur entomologists come across groups that no-one bothers with, I'm not talking about the flies, or even the spiders that us uninitiated seem to steer well clear of. I'm talking about the small groups that people for one reason of another avoid. In most cases its because they are ruddy hard and need genitalia excavation or are highly reliant on host/food plant identification, but sometimes its just due to a lack of freely available information.
Scorpionflies seem to fit into the latter category, and yet I still am not entirely sure why...
In the UK there are 3 main species of scorpion-fly: Panorpa communis, P.germanica and P.cognata, although apparently there is a newly introduced species by the name P.vulgaris. Now I'm by far an expert but I figured if there's only a 4 species they can't be that hard to differentiate, even by sure guess work the laws of probability denote a quarter chance of getting a correct ID.
A little digging told me that the key to ID's in this genus is either refer wing venation (which is also very variable and unreliable) or male genitalia.
Now usually male genitalia involves a microscope, a bent pin and some 'mad fishing' skills, but my scorpionfly homies have it out in plain sight:
You see that beast scorpion tail on the end? That's 100% pure Panorpa genitals, and now for the money shot:
Yes its a naff photo and when you whack it up on a big screen it looses its resolution...but the best bit? It's still good enough to use to ID!
Thanks to the magnificent guys at BugLife on twitter who threw me a lifeline to This lovely post by Martin Harvey, with some lovely images of the different species... but me I like all my info on the same page, so I dragged out my sketch book and dusted off my artist attire....
Here are the 3 main species: from just looking at the back-end of males we can clearly rule of P.cognata and P.germanica leaving us with the dynamic duo of P.communis and P.vulgaris (its never that simple)
Apparently we now have to look for the basal spot on the wings (the marking closest to the body). If this marking is larger than one cell (ie it crosses from one to another) its vulgaris.
If its contained in one cell and is either very small or virtually non existent it is P.communis.
Personally I feel this may not be the most accurate way to separate the two, but until I have both the time and opportunity to see some vulgaris specimens for myself or someone creates an updated key, thats all we have to go on!
In the above photo of a male We cannot even see a single basal spot, so we can say that this is likely to be P.communis!
Edit: I was shown this paper on Facebook, and it has some well snazzy images in it, (even if my french is limited to 'where is the egg?' ) including wing spot placement and adeagal diagrams.