Cluster flies on a window
Video. 17 sec. Near St Ives, Cornwall. October 2018
When I made this video I assumed that the flies that it features were house flies that had been feasting on a rotting animal carcass concealed somewhere within the walls of the building. The sinisterness of the insects was intended to be a feature of the video.
Since then a bit of research has informed me that the insects were in fact harmless cluster flies (pollenia rudis).
Cluster flies enter buildings on autumn evenings in search of shelter from the worsening weather conditions. Then the following day they sometimes want to get out again, as in the video.
They may enter buildings in small numbers or they may enter in thousands. In the case in the video it was many many hundreds.
The flies live in the countryside, where their larvae feeding on earthworms. They aren’t a health hazard (as far as I know).
Knowing that the flies were harmless and had entered the building seeking shelter rather than being house flies fresh from a rotting corpse in the attic altered my view of them considerably, and I now rather like them, at least on the video. They are an inconvenience though.
I particularly like the way that the flies in the video are moving in an almost choreographed manner.
The nice calm view out of the window (apart from a bit of wind) is in stark contrast to the dynamic motion of the flies on the window pane.