Why are flyspots SO hard to clean from ceilings?
The reason flyspots are so hard to clean from ceilings stems from the way houseflies eat.

A housefly lands on food and vomits on the food, this vomit is very acidic and breaks down the food. It then sucks up the vomit and broken down food, (flyfacts) so when it poos this is very acidic as well, when this sits on ceiling paint for a while it actually burns into the paint. When you try to wipe the fly poo off the surface, unless it is very recent it will not budge.

Why do I get unsightly rub marks on my ceiling when I clean off fly poo?

As mentioned before (above) fly poo, being acidic, burns into the paint, so when you use more vigorous rubbing and/or a harsher cleaner or textured cloth you will actually rub through the top layer of typical matte ceiling paint leaving shiny rub marks in the surface which are particularly noticeable when the light hits it at low angles (like early mornings)
We have a great product that removes fly spots and repels them from the sprayed areas. It uses the power of Pure peppermint and eucalyptus oils.