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Hi Tony thanks so far. Fungus was out of my mind, tis seems very well to fit to this phenomenon. ;)
But the Musca domestica or similar? :| With the yellow abdomen (compare to pic 2) I see here more a Syrphidae like Eristalis sp. or Helophilus sp.?
But I'm far away from beeing a specialist on biology or ID of some fly. Only a hobby photograph. So please can you or one of other here confirm or re-ID?
many thanks
Norbert