Flies are two-winged polluters that often invade our homes, more so in summertime. Excluding biting flies, all species of fly feed by vomiting saliva onto the surface of their chosen food, squishing it with their feet, and sucking up the mixture. This contaminates the food with bacteria from the body of the fly via its feet. This behaviour can lead to the spread of food poisoning, dysentery, typhoid or cholera in countries where these sicknesses occur. It's also known that the eggs of parasitic worms can be carried by flies.