Crane fly mimicry

by Matthew Cobb

This is another beast that popped up in my Twitter feed, though I can’t remember when.  In this photo by Abalone from Germany It looks like a wasp at first glance, but many things about it suggest that it is in fact a crane fly (you can just make out the left haltere behind the fly’s left wing).

This is in fact Ctenophora flaveolata, a crane fly that is found in woods in Europe, ” in the west from Norway and Great Britain to Spain and Italy, in the east from Finland, Latvia and northwestern Russia to northern Greece, Ukraine and adjacent Russia” according to crane fly expert Pjotr Oosterbroek.

This species is clearly mimicking a wasp. You’d keep away from this, even though it could do you no harm at all.  The ‘sting’ isn’t a sting at all, for more than one reason…

You probably won’t have noticed the part that I find particularly intriguing, which can be seen much more clearly on the next photo, also by Abalone.

 

You can see the halteres really well on this photo, but above all, look at those antennae! They are stupendous. And they immediately suggest (but do not prove) that this is a male. Which indeed it is. And that also tells us why this animal cannot sting. The sting is a modified ovipositor, so male hymenoptera (wasps, ants, bees and ichneumon) flies can’t sting you. It’s a naturalist’s trick to handle a whopping great big male hornet without showing the slightest trace of fear (no, I wouldn’t try it, either). The only thing that nasty-looking rear end could do would be to crap or mate.

And mating is presumably what the antennae are used for – tracking down the smell of female crane flies. About which, I suspect, absolutely nothing is known.

The antenna differ drastically between the sexes and between related species, as you can see here. In the left column (2-5) you have the male antennae of four different species, each from a different genus. In the right column (6-9) you have a female antenna of the equivalent species. The closest relative to Ctenophora flaveolata is shown in Figure 4 (this figure is taken from here, where you can find more information about these rather attractive crane flies).

Why do the species show differences in the shapes of the antennae? There may be a functional difference or – probably more likely – it may be either random variation or some correlated effect of a selectively-driven change in some other aspect of the animal’s morphology. Yet again, “we don’t know” is the right answer.