knowyourphrase.com - Meanings and Origins of Phrases
Note: The definitions for sayings can be found with ease, but finding the origins of phrases proves far more challenging. Looking back through history, it's tough to find the place or person in which a phrase has its roots. We are limited to what can be found in writings, such as books, poems, newspapers, and plays. Often times, phrases will be quoted from century old newspapers, or from plays that were done in the 17th century by playwrights like William Shakespeare.
The phrases that are quoted are likely already commonly known, and have their origins elsewhere. For instance, just because an idiom shows up in a newspaper from 1850, does not mean the idiom originated from that newspaper. However, what that does tell you, is that the phrase was being used since 1850, so its origins are at least more than 150 years old.
The origin of this phrase is unclear, but the expression seems to suggest how fragile these insects are. Flies do, for example, have fragile life-spans. In fact, the Center for Insect Science Education Outreach says: "The average life span of a fly in a Lab is 26 days for a female, and 33 days for a male." That's pretty short! Indeed, once a fly hatches from their pupal stage, it's not long before they drop dead.
A flies life is also fragile once they buzz their way into a person's home. When they are spotted by the people living inside, flies usually don't last very afterwards. All it takes is a determined person armed with a flyswatter and these insects start dropping rapidly in number. Fragile, indeed!
An early recording of this phrase is written in an article from The Atlanta Constitution newspaper, printed in 1902, under the subheading "Men and Women Dropped Like Flies and Flames," and it reads:
"I saw women and men rushing back and forth amid the flames for an hour. They would run along, then
came the choking smoke and they would drop like dead flies."
The details in the quote above come from a terrible volcanic eruption that occured in the town of St. Pierre on that year.
Reference: newspaperarchive had a digital copy of the newspaper with the expression in the quote above.
A swift decrease in numbers due to an unexpected illness or death.
Example: If several staff working at a local store suddenly became bedridden with the flu, one might say the employees working there are "dropping like flies."
* One of my co-workers came in sick and accidently infected everyone with a terrible illness, so the amount of people available for work the next day dropped like flies.
* The ants marching around Ray's house were dropping like flies once he pulled out a can of bug repellent and started spraying them.