Flies can carry salmonella, dysentery, TB, cholera and parasitic worms. They’re both unsanitary and stupid.
Everyone gets one or two flies in the kitchen in summer, bashing their brains out two inches away from the open window they just came in.
But if you’re plagued by swarms of flies, you need to seek an underlying cause.
A plague of bluebottles may indicate there’s something dead in the house, possibly a mouse you dispatched earlier.