Monday, September 26, 2016

Mysterious 'bluebottle'

I recently found a rather strange and distinctive fly in our garden that turned out  to be Stomorhina lunata a member of the Calliphoridae, the bluebottle family, though it does not look anything like a bluebottle and has been compared to some of the hoverflies.

(There are many better pictures on line).

Widespread in England, especially the south, it is said to be scarce, though Steven Falk has found it in many locations on the South Downs in recent years.  Most accounts say that it is probably a migrant from mainland Europe or even further afield.

In Africa the species is known to breed in the egg cases of locusts and some suggest that it turns up in Britain when large swarms of locusts are on the march in Africa.  This hypothesis has metamorphosed into the idea that since the early stages have only ever been found in locust egg cases, the adults must be migrants in the cooler parts of Europe - a good example of the absence of evidence being taken as the evidence of absence (in this case of the fly breeding in Europe).

In this Internet age, the Food and Agriculture Organisation of the United Nations monitors locust swarms and there does not appear to have been anything exceptional, or close to Europe, in 2015 or 2016 (  I therefore suggest that Stomorhina lunata can breed in places other than locust egg cases, though maybe in mainland Europe rather than the UK, so our records could still be of migrants.

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