All flies have a rapid rate of growth and go from egg to adult in about seven days. Maggots are just one stage in the early development of a fly. Maggots of some fly varieties, such as the Carrot Rust fly, can be a problem because they eat the roots of some vegetables. The most common flies are the Fruit fly, the House fly (which have four stripes on their abdomen), the Cluster fly (which is dark gray in color), and the Garbage fly (which has a metallic color that is either green or blue). Another kind of fly, the Stable fly, typically exists around livestock. The Horse fly and a few other varieties of flies actually have mouth parts and can bite humans. Most other flies have a sponge-like mouth and can only drink up their food.
One benefit of flies is that they help reduce the population of other pests. They also help to break down carcasses and other decaying matter faster by preparing it to reenter the ground. Properly controlling flies includes not only killing the adults, but also destroying their eggs and larvae. Call a pest professional to manage any fly problems you encounter.