Insects breathe in a way that is very different from us. Instead of having a central place to gather and a transport system to deliver the oxygen to all of the cells of the body like us, insects have a system of fine branching tubes called a tracheal system that delivers the oxygen directly to each cell in the body. Imagine that you are an oxygen molecule in the atmosphere and you are about to be "breathed" into an insect.
Though houseflies are rulers of the insect-scavenging world, they have many predators just waiting for a chance to gobble them up. Spiders, frogs, lizards, sparrows, wasps -- even members of the plant kingdom -- want a slice of the housefly pie. On top of that, disease-conscious humans try to shut houseflies out or exterminate them once they're inside. To help overcome all these obstacles, houseflies depend on excellent sensory awareness and top-notch aerial maneuverability.
The housefly's thorax features all of its limbs used for movement. Though flies appear to have only one pair of wings, closer inspection reveals the presence of tiny, secondary wings, called halters, located below the main pair. While their ancient ancestors boasted two full sets of wings, houseflies have learned to do more with less. Over millions of years, the lower set evolved into the shrunken appendages you see today. They're far from useless, however. Houseflies flap their halters at high speeds during flight, using them to maintain balance in the air. If one halter is removed, the insect can only fly in circles. Without either halter, the fly can't take to the air at all.
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