Friday, 25 October 2019

Cluster Flies


One day I visited friends in the next valley and was surprised by the level of buzzing coming from the vicinity of their front door. At first I assumed it was late season bees in the Russian Sage but then I realised it was dozens of golden haired flies.

Female cluster fly.
Female cluster fly Pollenia sp, Indre et Loire, France. Photographed by Susan Walter. Tour the Loire Valley with a classic car and a private guide.

The identity of these flies wasn't much of a mystery. The golden hairs make them unmistakable as cluster flies Pollenia sp. They are parasites of earthworms and will have mass emergences from time to time, especially if there is well rotted cow manure around to attract earthworms and therefore the flies. That was the case here, as a few days earlier the neighbouring farmer had been muck spreading.

Male cluster fly.
Photographed by Susan Walter.  Tour the Loire Valley with a classic car and a private guide.

The flies can be a bit of a nuisance, in that they come indoors to hibernate in nooks and crannies, and where they will die in large numbers on windowsills and in attics. They are not attracted to human food so do not represent a health hasard, but once they are present in a house you will likely never get rid of them, as each new generation seems to return to a favoured location. I can remember housesitting at Tyntesfield in England before the National Trust opened the property to the public. Crossing the floor in the attic was to crunch across a carpet of cluster flies that had accumulated over several years.

Cluster flies on the exterior of the house.
Photographed by Susan Walter.  Tour the Loire Valley with a classic car and a private guide.

There are 18 species of Pollenia in France, not very easy to identify to species level. These are probably the most abundant species, the Common Cluster Fly P. rudis (Fr. Mouche des greniers).

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2 comments:

Jean said...

We had an inundation of flies last week, a hatching from somewhere in the house. Having hoovered up all the dead ones in the spare bedroom windowsill we then watched carefully to see if we could spot where they were coming from but no, they just appeared in the window as if by magic. A real nuisance.

Unknown said...

That was an annual occurrence in our previous house, and after the flies would come an army of ladybugs. I was always curious about the connection.
Jocelyn

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