Did that little buzzer just vomit on your meal? It's even weirder than that. Here's exactly what happens when a fly lands on your food.
The Gross Reason You Might Not Want to Eat Food If a Fly Lands on It
Nobody likes flies buzzing around or—blech!—landing on food. It’s disgusting, for sure, but is it harmful? A study on what happens when a fly lands on your food found it’s more than gross: It’s germy.
But does that mean you need to throw out your sandwich, or can you shoo the buzzing bugger away and keep chowing down? As a health reporter, I wanted to know exactly what happens when a fly lands on your food. So I went straight to a public health epidemiologist and an entomologist (aka an insect expert) to get the poop. And yes, there’s poop—and other bodily fluids—involved.
Keep reading for some weird facts about flies that’ll help you understand what these critters do when they land on your food, whether it can make you sick and how to react when a fly inevitably touches down on your dinner.
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What happens when a fly lands on your food?
You may have heard that when a fly lands on your food, it vomits. Surprise: This internet rumor is basically true.
“When a fly eats, it has to throw up digestive enzymes onto the meal,” says Brian Labus, PhD, assistant professor of epidemiology and biostatistics in the School of Public Health at the University of Nevada, Las Vegas. “These enzymes also contain some remnants of whatever it last ate, and that might have been a meal full of pathogens. Flies eat some pretty disgusting things.”
But let’s back up: Before the fly vomits, it “uses its antennae to sample your food with taste sensors on its feet,” explains entomologist Julian Shepherd, PhD, professor of biological sciences at Binghamton University. If it likes what it tastes, it sticks down its tongue—its official name is the proboscis—and coats your food with saliva containing digestive enzymes (a form of puke).
Are you grossed out yet? This detail may do it: “The fly also poops liberally on your food,” Shepherd adds. Got to love amazing science facts. Some good news on the No. 2 front: “It’s such small amounts,” he says.
What kinds of diseases can flies spread?
Here’s something else that can happen when a fly lands on your food: It can spread salmonella, E. coli, parasites and dysentery. A 2023 study published in the journal Microorganisms found flies can pass along bacteria, including antibiotic-resistant strains. “House flies serve as a vector to move disease from one place to another,” explains Labus, who was not involved in the research. “Because we live together, they can spread many different pathogens between humans, animals and the environment.”
On the upside, a fly can share only a tiny number of germs. And fortunately, when it comes to food poisoning, the dose makes the poison, as the old saying goes.
So when should you worry and throw out your food?
Sometimes that pest on your pasta can spread enough germs to make you sick, but “often they just start a chain of events that makes it possible to become ill,” Labus explains. There might not be enough bacteria initially coming out of the fly to do harm, but if you let the food sit out at room temperature for a long time, those bacteria can multiply to the point where they become dangerous.
What happens when a fly lands on your food after it has been dumpster diving? That’s a red flag because a trash bin is an “obvious source of contamination,” Shepherd says. You should also steer clear of eating if the fly has touched down on raw meat or animal poop before visiting your dish.
Of course, knowing where a fly has been before setting foot on your food can be tough. So the best way to minimize this (icky) problem is to keep flies away.
How can you protect your food from flies?
Simple measures like using window screens and hanging nontoxic, sticky flypaper traps can prevent these pests from setting up shop in your kitchen. At picnics and barbecues, keep dishes covered as much as possible. Also key: “Make sure that foods are kept at the right temperature and don’t sit out too long, as that can turn a small problem into a big one,” Labus says.
What other insects should you worry about buzzing around you?
There are worse critters to find circling your plate because they could land on you and lead to big health problems. Mosquitoes can bite you and transmit West Nile Virus. What’s worse, they can give you malaria, yellow fever and dengue fever, which are “not of great concern in North America yet, but climate change will change that,” Shepherd warns.
And ticks are capable of transmitting many diseases beyond Lyme. “In many parts of the U.S., ticks can transmit Rocky Mountain spotted fever, anaplasmosis and babesiosis, all life-threatening if untreated,” Shepherd says. That’s why he tells his students: “Hey, don’t worry about flies so much. Worry about mosquitoes and ticks.”
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At Reader’s Digest, we’re committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers’ personal experience where appropriate. We verify all facts and data, back them with credible sourcing and revisit them over time to ensure they remain accurate and up to date. For this piece on what happens when a fly lands on your food, Lisa Lombardi tapped her experience as a longtime health reporter and the author of What the Yuck?! The Freaky and Fabulous Truth About Your Body to ensure that all information is accurate and offers the best possible advice to readers. Read more about our team, our contributors and our editorial policies.
Sources:
- Brian Labus, PhD, MPH, assistant professor of epidemiology and biostatistics in the School of Public Health at the University of Nevada, Las Vegas; email interview, Sept. 12, 2024
- Julian Shepherd, PhD, professor of biological sciences at Binghamton University; phone interview, Sept. 12, 2024
- Microorganisms: “House Flies Are Underappreciated Yet Important Reservoirs and Vectors of Microbial Threats to Animal and Human Health”
- BMC Public Health: “A Systematic Review of Human Pathogens Carried by the Housefly (Musca domestica L.)”
