Bluebottles

The Bluebottle is a large buzzing fly with shiny, metallic blue body, 6-12mm long.  One Bluebottle can lay up to 600 eggs, which in warm weather will hatch in under 48 hours and produce maggots which can become fully developed in a week. These maggots burrow into meat or carrion as they feed on it, and then pupate, often in loose soil, for about ten days before emerging as adult flies from the brown pupal case. Bluebottles, like other flies, are often found around refuse tips, rotting animal matter, dirt and dustbins. They commute from filth to food, and carry bacteria on their legs, feet and bodies.

Keep meat and other food covered. Use an insecticidal dustbin powder. Indoors, use an aerosol flyspray. Consider fitting fly screens over kitchen and dining area windows.