When you're eating outdoors and a fly lands on your food, what do you do? I'm guessing you do what we all do, you brush it away and go right back to eating. THIS might change your approach. It turns out what within the first few seconds of a fly landing on your food, it starts VOMITING digestive fluid on it, according to Sometimes Science. The fly is trying to get it soggy enough that it can slurp it up, since it doesn't have teeth.
Flies aren't exactly sanitary bugs. You know how you see them buzzing around manure? They're slurping that up too. So when a fly throws up on your food, even though it's a tiny amount, they could be spreading dangerous bacteria onto it including salmonella and E. coli. Not every fly is going to contaminate your food. But they COULD. And babies, elderly people, and people with weaker immune systems are most susceptible. So what can you do? When you eat outside, keep the area trash-free the trash attracts flies. If possible, use citronella candles or other repellents.