TheLandscapePainter I did one painting at summer outside, flies somehow did not bother me, it was a day time, not evening though...
I had a tiny fly stick to the wet paint on one of my seascapes and i had to wait till it dries. While it was drying it was looking like another seagull 🙂 I removed it without problems when it dried.
Wind is another issue that can bring sand and flip the canvas...
and to add to the list - carry ready masterpiece home is something of a challenge if one has no car.
I seriously think to take a garden trolley and put my supplies, chair and little table in it and walk to the painting site. It is apx 20 min walk for me. I plan no easel and just paint on the table to remove issue of flipping canvas in the dirt together with easel.