Scientists Say Food We Eat Can Be Toilet for Flies

Flies, just like nearly every other creature, vomit. They poop, too. And yes, whenever they land on your food, they do both.   

The icky stuff they leave behind contains pathogens from what they’ve consumed: rotting food, animal poop, roadkill perhaps. (Sorry if we’ve ruined your breakfast). 

“It’s gross to learn about these things and to think about them,” Lyric Bartholomay told The Washington Post. She's the director of the Midwest Center of Excellence for Vector-Borne Disease in Wisconsin. “But I think there would be a lot more people a lot more ill if flies were transmitting high doses of these pathogens.”   

Experts say fluid left behind from a couple of flies on your doughnut probably won’t hurt. But leave it out long enough for the tiny bacteria to multiply or to allow other flies to join the feast, and it might.     

It also depends on the type of pathogen left behind. Just ten organisms of the bacteria shigella could make someone sick. By contrast, it takes 50,000 salmonella organisms to make someone sick, experts say.   

A 2022 University of Massachusetts study, though, found that people should pay more attention to “synanthropic” flies. Those are the ones that don’t bite but land on our food and skin. That’s because they don’t digest food like other animals. Instead of a stomach, they have a "crop." It stores food for energy. But it doesn't kill bacteria. So those pathogens can get passed on.   

“It’s the little things that cause the problems,” John Stoffolano said. He's a UMass Amherst entomology professor and study author. “Our health depends on paying closer attention to these flies that live with us,” he said. 

Reflect: What small things around you might affect your health, and how can noticing them help you stay healthy?

Photo of a fly from Unsplash courtesy of Chris Curry.