Why Are Flies Attracted To Poop?

There's a pretty famous expression in relation to flies on poop, though it usually involves a ruder word than "poop." The idea that flies just can't help themselves around feces is one that's so ingrained in our collective consciousness, we probably haven't ever questioned it. Flies like to swarm around the grossest stuff, after all, from overflowing trash-cans to dead animals and rotting produce. However, as Western Exterminator notes, flies are also fascinating creatures. They breed, feed, and move completely differently to humans.

For instance, houseflies typically exist on a liquid diet because they can't chew solid food. As the site explains, they "regurgitate digestive juices onto solid foods and these juices break down the food into small pieces, allowing them to use their mouth-parts, called proboscis, to drink the meal." Flies actually taste with their feet, because their receptors, or chemonsensilla, are located there. So, flies land on something to eat it, essentially.

As Western Exterminator explains, when a fly lands on something yummy, whether it's your food or something else, "They will often wander around to give their next meal a good taste before consuming it." Flies also tend to lay their eggs on anything from feces to rotting fruit and carcasses, so their larvae, or maggots, have a meal waiting for them when they hatch. This, naturally, means flies are very unhygienic. They can spread all kinds of horrible bacteria, including salmonella and E. coli, simply by landing on food or cooking utensils.

Put simply, as an answer on Quora advises from Matan Shelomi — who has a PH.D. in Entomology — poop smells really good to flies. A commenter on Reddit, meanwhile, notes that flies are generally attracted to feces because of the nutritional value. It's advised that "Feces contain large amounts of dead and alive bacteria, fats, proteins, indigestible carbohydrates (like cellulose — fiber!), minerals, and trace amounts of other nutritious goodies." Although there's no nutritional value for us, flies have their own specific needs. To them, feces represent a nutritious meal,as well as a safe place to lay their eggs.