[katieHaylor (OP)]

Rhys says:

Given that black is not a good camouflage colour for a housefly, could it be that it has a partially thermal "solar" driven flight engine with the black body acting as the heat absorber?
I read recently that scientists were surprised to find that their wings had blood vessels. The rapid movement of the wings in flight would make extremely good heat radiators cooling the blood. It may be that the flow of cooled blood through the flight muscles actually help physically with contraction and thereby assisting with flight and supplementing the energy derived from feeding.

What do you think?