Flies in paradise, flies in your food, flies on you drinks, flies in your face, flies on your hand, flies on your legs, feet and other unmentionable places, the South Pacific is flies. Seems to be no connection between areas with no village, and ones of with villages . The largest village we visited had almost no flies.
We have screens on the doors, but I'm not sure it helps any at all. I know they get in by hanging around the back porch and then hitching rides on people coming and going. I wonder if the screens hold them in? Maybe they just stop in and can't get out. The only effective fly control is an extra large swat that Martha bought in NZ a couple years ago. A single fly will pick out a person and that person must leave the boat or kill the fly, no peace pact is possible. Constantly during the day one of us will spend 20 or 30 minutes chasing flies around the boat, doesn't eliminate them just keeps irritation level at a point that we can live with. Sometime we don't succeed and Martha or I go off the deep end and declare war and spend an hour chasing flies, cursing each one as we bash it with the swat. You never get them all. When you go to bed at night they come out of someplace and really get irritating.
We are all concerned about malarial mosquitoes and most take preventive medicines, cover up in the evenings, use repellents, long sleeves , ect, ect. I suspect that these flies carry stuff that makes malaria seem like the common cold.