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I would like to know which species this is
It concerns this sighting
http://scheldelan...w/87569361
identification uncertain Unidentified Fly - Diptera indet. observed at 2014-08-29 Laarne - Centrum en omgeving
Photos:




thanks in advance Luc

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It seems to be a dark Episyrphus balteatus.

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Sure it is. Female E. balteatus.

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Just for info, there can be 3 main types of E. balteatus: the "usual" one (which is the one often seen), a "light form" (with tergites extremely poor in black stain) and the "dark form" (rich in black stain) i.e. is the case of these photos.

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Thanks, very interesting and first time I see a different one.
Are these dark versions rare?
Luc

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The colouration depends of the temperature during pupal stage. Warm temperatures make lighter coloured forms, cold temperatures make darker coloured forms. Darker forms better retain the heat.

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Here, in Italy, I've never seen one (and consider that in my experience E. balteatus is the most abundant hoverfly). But I know about them from North European papers, and this easily confirms Stephane's speech.

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Come in North of France, you'll see ones ! August was just as warm as October.

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Here is an extreme example photographed in December in the south of France.

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Incredible. It's near full melanic In pictures I've seen they're never so dark. South France should be somehow similar with its climate to North-East Italy. This autumn/winter I've to try to find some.

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They all look like intersexes: most markings obscured, frons narrower than in regular females and no distinct genitalia.