The war against flies began in earnest in the early 1900s when it was discovered that typhoid fever was being caused by flies spreading Salmonella typhi to humans. Screens were installed to keep flies out of doors, and the fly swatter became the weapon of choice in almost every home and business in America. The idea for the fly swatter originated with the health officer of the State of Kansas, Dr. Samuel J. Crumbine. While attending the opening day of the Western League baseball season in Topeka, the doctor had a brainstorm. The score was 2 to 2 in the 8th inning, with one out and a Topeka runner on third.
Flies carry more than typhoid fever.
Because they breed in sewage, garbage, manure and human feces and feed on these same sources, flies carry all sorts of disease-causing organisms, including Salmonella and E. coli. The fly can only consume liquids so when it lands on food it first spits some intestinal juices onto the meal to make it liquid and then consumes the liquid through its proboscis. Not being very fastidious, the fly leaves behind a sampling of whatever bacteria it may have ingested or gotten stuck on its six hairy legs at its previous feeding. But you can appreciate his motivation. The rat and mouse are pests that wreak havoc on public health and the economy like no others.