Walking the market with my father-in-law he was surprised by the amount of flies on certain foods. I find it annoying when a fly is eating what I intend to eat.

A fly tastes with their feet, so they have no choice but to walk on your food. When a fly comes upon something that seems like it finds interesting, it will reflexively stick out its labella and press it against the potential food item to investigate. Liquids can be slurped up without much effort however, if they come upon a desirable solid such as meat, they employ a process which renders the food into a liquid. After scraping the solid food into flakes, a fly will essentially vomit saliva and digestive juices onto the intended meal and wait for it to be broken down into a softer, more liquid state.

Flies vomit and poop when they land on foods but not every single time they land. It really depends on whether or not the fly thinks you are a potential meal. If the fly gets a message from its feet saying, “yes” this is a delicious opportunity, tastes pretty good, then the recipient gets a little fly liquid vomit.

Anytime you vomit repeatedly, you run the risk of dehydration, so you have to drink a lot of fluids to replace the ones they lost. And when you drink a lot of water, what goes in, must come out.