Everyone has seen the little critters: they fly around, climb up and down walls, and generally make themselves a big nuisance. It's the housefly, and if you look at them closely you can understand how insects can climb on a wall that no human could. Flies are just like most insects; they have six legs and three sections to their body, a head, a middle section called a thorax, and a hind section that is called the abdomen. Since flies fly, they have wings as well.
But how do they climb on walls? It helps to imagine what it would be like if we were a fly. Let's say we suddenly shrunk down to the size of a fly. Everything would be about 150 times bigger! Suddenly a piece of paper would be around the size of a 12 story building! If we walked over to a wall, we would notice that instead of a smooth surface, it actually looks bumpy and rugged. That's because everything we use, from wood to plastic, has some kind of a roughness to it. But if the roughness is small enough we don't notice it. Since we are still the size of a fly, when we go to the wall we find that it is made up of bumps and crevices about the size of a small doorknob. So if we were the size of flies, with a little effort we could climb walls too. Flies don't have hands, instead they have little hooks at the end of each of their feet. In addition, for smoother surfaces they have little sticky pads which not only help them to walk but act as tastebuds. So everytime a fly walks around, it's tasting what it's walking on! This helps the fly to find food and places to lay its eggs.
There are lots of fun facts about flies and most of them can be found either on the web or at a library near you. The one bad thing about flies (besides being annoying), is that they can carry harmful diseases. The best way to avoid having flies around is to keep everything clean and dry.
Little Lions Experiment:
Now you can see for yourself the ways a fly can walk around on walls, glass, and ceilings. Take a piece of paper and fold it into quarters. This will be your "wall." Arrange the paper so that some of the folds are peaked like mountains and others are down like valleys. This is similar to how a wall would look to a fly. Take something smooth like a ceramic tile or a coaster and place it next to the paper. Now take your pointer finger and make it into the shape of a hook. You now have a fly leg! Drag it across the paper and the tile. Next take a piece of tape and with the sticky side down drag it across the paper and the tile. Which works better on the paper? Which works better on the tile? Why do you think a fly has both?