Catch them all and express mail to PETA.

Domestic flies are not only a nuisance by their presence, but are important from a human and animal health standpoint. House flies may spread diseases such as conjunctivitis, poliomyelitis, typhoid fever, tuberculosis, anthrax, leprosy, cholera, diarrhea and dysentery. They may serve as intermediate hosts for parasitic tapeworms on poultry or parasitic roundworms on horses. Certain larvae of blow flies, bottle flies, screwworm flies and flesh flies may feed on dead as well as living tissue of mammals, causing blood poisoning and even death, especially in sheep. Stable flies bite painfully, sucking blood from humans and animals.