The housefly belongs to the Arthropoda phylum; its class is Insecta, and its order is Diptera, "meaning two-winged." Arthropods are defined as:
...animals with exoskeletons (external skeletons), segmented bodies, and jointed legs. They are the largest group of animals on Earth and include insects, crustaceans, and arachnids.
The three major parts of a fly are the head, thorax and abdomen.
The fly has two "compound eyes" that cover a good deal of the fly's head. The eyes are found on the sides of the head, and are "purple-brown in color."
The surface of each eye is divided into about 4,000 facets.
Flies have three "simple eyes" between the larger pair of eyes, and a pair of antennae on the head as well.
The thorax is the part of the torso that provides for wing movement and " equilibrium during flight." The abdomen fills with food; also on the abdomen the female has a "segmented ovipositor," which is used to lay eggs.
Flies are interesting for several reasons, despite the abhorrence many feel at their presence. Flies have eyes that are "the most complex in the insect world." Flies taste not only with their mouths, but also with sensory parts found on their feet. Their feet also have a sticky "soft pad" that allows them to walk on horizontal or vertical surfaces. Flies, despite the unsavory means in which they eat and grow from a larval stage, are fastidious in nature, endlessly cleaning themselves.
While flies help in the natural decay of dead animals, this very fact also contributes to the insect's spread of disease to humans. Flies live only between seven and ten days in the warmest months of summer (in "temperate areas").