House flies eat things such as decaying matter and feces. They also feed on garbage, spoiled meat and rotting fruits.
Common house flies are a nuisance and according to Penn State College of Agricultural Sciences, they can transmit over 65 different diseases to humans and animals. The flying insects rarely grow larger than 1/4 of an inch long and they can only ingest liquids. To turn decaying matter and solid food into a liquefied state, they throw saliva up on the food source. The saliva then liquefies the food so that the flies can suck it up using their proboscis.