Do House Flies Poop?

Written by Kristen Holder
Published: May 24, 2022
Image Credit Fotopstryk/Shutterstock.com
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When flies are buzzing around your home, it’s easy to wonder what they’re doing and how they do it. These pontifications can turn into the most basic and hilarious of questions. Do flies, particularly houseflies, poop?

Flies are such a ubiquitous nuisance that there are tons of products on the market to help us avoid them. These insects don’t have a long lifespan, but they breed profusely, so it’s hard to tackle a fly infestation unless you’re able to contain the source.

Despite this, flies are vital to the ecosystems that surround us. They help in the process of decomposition, they’re pollinators, and they’re a good food source for other animals. Flies are just about as vital as bees when it comes to crop success. They’re also culprits in the spread of shigellosis, cholera, typhoid fever, and E. coli. That’s because they aren’t hygienic and frolic around in pretty disgusting places.

Why are they not hygienic? Does this have to do with poop? Do house flies poop? Let’s find out!

Do Flies Poop?

isolated housefly
Flies poop waste from digestion out of their anus.

iStock.com/Pattra Jayasvasti

Yes, flies poop. They eat food that is digested in their stomachs. Any leftover waste created by their digestive tract that their bodies can’t use comes out as excrement through their anus.

It’s believed that they poop every time they land. Since they eat nothing but a liquid diet, their poo is runny and it’s created quickly. That means that the housefly buzzing around your house is pooping on every surface it touches including curtains, walls, food, bed sheets, and your face.

This is one of the many reasons that flies are considered nonhygienic. Their food sources are full of pathogens that affect humans, and they leave their poop wherever they go. 

Do Flies Pee?

No, flies do not pee. Technically, they poop and pee at the same time. Since all of it comes out of the anus at once, it’s poo, not pee. Flies do not have a separate system that produces urine. Instead, they produce uric acid, which is a solid that is released with their feces.

Before modern medicine, one of the ways to diagnose someone with diabetes was to leave out their urine and see if flies were attracted to it. If flies showed up and made a meal out of the pee, there’s sugar in the pee. This is a major symptom of untreated diabetes.

Do Flies Fart?

housefly on green leaf
Flies may fart and produce gas during digestion.

IamBijayaKumar/Shutterstock.com

Flies might fart. They produce gas during digestion, but whether they fart out of their anus is up for debate. Not many studies are available about the type of gasses produced in insect digestive tracts. They may fart when they defecate.

On the other hand, the digestive gasses might be reabsorbed by their blood and released through holes in their exoskeleton. These holes are also used for breathing, though they aren’t farting out of their mouths. Their mouths are a separate part of the body used for eating.

One piece of evidence that flies do in fact fart comes from flies fossilized in amber. Gas bubbles are coming from their anus which is preserved in resin for all eternity. The bubbles have been studied closely and were not created through other means like decomposition.

Do Flies Barf On My Food?

Yes, flies barf on your food. The reason a fly vomits on a food source is to release digestive juices since they eat a strictly liquid diet. Sometimes they’ll hold what they’ve slurped up in their mouths before vomiting it out again until it’s the right consistency.

Flies aren’t able to chew so the food has to be liquidy enough for them to suck up through a straw-like mouth. This mouth is known as a proboscis, and it contains no teeth.

Using juices to digest food before it’s swallowed isn’t unique to flies. We do it, too. Our saliva, combined with the act of chewing, begins the digestion process before we swallow what we’re eating. In this small way, we are the same as flies.

Can I Still Eat Food if a Fly Lands on It?

What Do House Flies Eat - Flies Eating
Flies are not hygienic because they eat poop and rotting meat.

iStock.com/reto_s

It’s not safe to eat food on which a fly has landed. That’s because flies make a dinner out of unsanitary things like rotting meat and feces. They easily spread salmonella, worms, and E. coli due to their propensity to bounce from food source to food source.

Flies have hairs on their legs that trap all kinds of things. That’s why they make such great pollinators, but it also makes them rather disgusting. They can get animal poo flecks or even worse items all over your food simply by landing on it.

Flies will also lay eggs in your food if you give them half a chance. These eggs hatch in a few days, creating maggots, which is one of the most disgusting things anyone can find in something they’re about to eat. Keep in mind also that they poop on every surface that they land on.

A study of street food in Burkina Faso showed there was a prevalence of contaminates in food found where flies were thriving in waste. Since waste wasn’t contained and was in proximity of the food, the food was contaminated with diseases like Shigella, and streptococci through flies.

Cockroaches are technically cleaner than houseflies. Would you eat food if it had roaches on it?

Why Do Flies Eat Poop?

Flies eat poop because it contains partially digested food that they can consume. It’s also a great spot to deposit eggs for the same reason. When their eggs hatch and become maggots, poop is the perfect food source because the nutrients around them aren’t complex.

Flies love the smell of poop, which is why they’re attracted to it. Poop contains fats, proteins, and minerals that provide a balanced diet to a fly. Any wet garbage or decaying corpses are also prized fly food. They enjoy bird feces because it’s already in liquid form. Flies still barf on the bird poop to start the digestive process like they do with everything else. This allows them to slurp it up through their proboscis with minimal work.

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About the Author

I'm a freelance ghostwriter that specializes in SEO content. I have always loved writing, and when COVID happened, I went at my passion full tilt. I'm currently in Spokane, WA by way of Phoenix, AZ, though I'm originally from Sacramento, CA. Freelancing allows me the freedom to move around as I please.