A blog about birds, insects, in fact any kind of wildlife. Mostly around Topsham, Devon. Photos, sketches and illustrations.

Friday, 21 May 2010

Scorpion Flies

There are some spectacular insects lurking in our hedgerows, albeit on a small scale. Scorpion Flies are particularly exotic looking beasts; yellow and black with patterned wings and a prominent beak. Males carry their swollen ‘tail’ curved over their back very like a scorpion. Although it may look menacing there is no sting in the tail - it’s there for mating. Scorpion flies (order Mecoptera) are easy to find in hedges and woods, often sitting motionless only to disappear when a lens is focused on them. They are mostly carnivorous and seem to prefer dead to living insects, I’ve seen them feeding on tiny flies and much larger bumblebees (which surely must have been dead already - see photo below). There are officially  three species in Britain (Panorpa communis, P.germanica and P.cognata), although the unproven presence of a fourth, P.vulgaris, has been suggested (Plant, 1997).



All three species are very similar but, in the males at least, can be identified with fair certainty by examining the ‘sting’ at the end of the abdomen. The important characters are very hard to see in the field but can be checked on good close-up photos. On the lower (ventral) surface of the genital capsule (the swollen bit) is a pair of  structures known as hypovalves (photo below), these differ in shape in the three species as follows:


Panorpa germanica – hypovalves  parallel or slightly diverging, expanded at tip - as photo above.

Panorpa communis – hypovalves  slender, not expanded, curving out and then converging at tip.

Panorpa cognata – hypovalves  slender, not expanded, diverging at tip.


Because male scorpion flies helpfully hold the tip of the abdomen curved over, the ventral surface is actually the upperside as seen in the field.

After checking as many scorpion flies as I can photograph, I find that germanica is the commonest in my area of Devon, with occasional communis – even in the same hedge. I’ve yet to find cognata. P.germanica males are abundant as I write this (mid May) with females appearing in the last week or so. This female (presumably germanica) is feeding on a Bibio marci carcass.


It is rumoured that P.vulgaris may occur unnoticed in Britain, although I can't find any stated reason other than that it's common just across the channel. The shape of the hypovalves is virtually identical to those of communis, the only difference apparently being the more heavily spotted wings of vulgaris (Tillier, 2008). To describe these differences accurately I'm afraid we’re going to need some more technical terms: the next photo is a wing of P.communis.


P.communis – wings lightly spotted, basal spot small or absent, submedial band narrow and always divided into two parts, marginal spot small and narrow, pterostigmal band narrow and incomplete – never a complete ‘Y’, as photo above.

P.vulgaris – heavily spotted wings, basal spot large, submedial band large and complete, marginal spot large, pterostigmal band usually large and ‘Y’ shaped.

So I'll be looking carefully for any communis lookalike with well spotted wings.

Refs:

Plant, C.W. 1997. A Key to the Adults of British Lacewings and their Allies (Neuroptera, Megaloptera, Raphidoptera and Mecoptera). Field Studies, 9, 179-269.

Tillier, P. 2008. Contribution à l’étude des Mécoptères de France. Deuxième partie : clé de détermination des Panorpa de France (Mecoptera Panorpidae). L’Entomologiste, 64, 1, 21-30.

3 comments:

  1. Thanks for this post Tim, very helpful. I've added a link to it on iSpot:
    http://www.ispot.org.uk/node/138025

    ReplyDelete
  2. Thank you very much for this post, helped me and others more than once (or twice)
    Vilia D., Copenhagen, DK

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  3. Tim - very good work, most useful, thanks.
    I have made reference to it in two scorpion fly ID questions on the NaturePlus (NHM) website
    http://www.nhm.ac.uk/natureplus/message/34196#34196
    http://www.nhm.ac.uk/natureplus/message/34198#34198

    Regards,
    Mike Hardman

    ReplyDelete