Flies may be yucky, but they are also amazing organisms.  Why do flies always land on your food?  If they were trying to eat it, wouldn't they put it into their mouth?  The truth is, when a fly lands on your food they can already taste it.  Flies have very, very small hairs on their feet that let them taste what they're standing on, just like the taste buds on your tongue help you to taste your food.  These hairs help them to smell, feel and taste their environment.  They fly around tasting everything they can to find food and a place to lay their eggs.  

            Flies have to find a way to stay safe because they are so small, and very easy to hurt or kill.  Flies are always flying (it is their name, right?) and you probably won't see them sitting still for very long.  If a fly stopped moving a person could swat it, or a spider could eat it.  The more they move, the safer they are because they're too fast for people and spiders to catch.  They taste with their feet so that they never have to sit still for too long.  Imagine if you could go to the store and walk around on the food to decide what you wanted to eat instead of picking it up and smelling or looking at it.  Shopping would be so much faster!