House flies eat their own vomit.
Houseflies use their feet to taste things because they don’t have mouths to bite or chew food. If they find something yummy, they vomit on it because the puke contains digestive enzymes that help to break down the food. The vomit allows flies to use their sponge-like tongue to soak up the barf and get the nutrients they need. Make sure you know which seemingly “harmless” bugs can actually bite you.