You might want to throw away your food if a fly lands on it, because they’re slobbering, vomiting and pooping all over it. They can also transmit more than 100 different diseases.
According to a study done in 2017, flies usually spend their time in garbage and animal waste, where they pick up pathogens on their legs, which will transfer to whatever surface they land on. Flies also have no teeth, so they eat by spitting and throwing up on their food. A compound in their saliva and vomit breaks down the food so the fly is able to slurp it up. As a fly eats, it usually poops, and if it’s a female, it might lay eggs, too.
The longer a fly is on your food, the higher the chance of harmful bacteria, viruses and parasites being transferred to it. If a fly lands on your food and you swat it right away, the food will likely be safe to eat. But, if you want to play it safe, and better ensure that no horrible pathogen ended up in it, you might just want to throw it away. Flies are annoying to begin with, but learning what they’re capable of doing to your food makes them even more undesirable.