Flies are generally common and can be found all over the world except Antarctica. Many species are particularly important as vectors of disease in man, other animals, and plants. Since that time they have diversified to become one of the largest groups of organisms. An equal number of species may await description and most of these will be found in environments that remain to be studied intensively, such as tropical forests. Flies are holometabolous insects, that is their life cycle involes a major change in form from a soft-bodied, wingless larval stage to a hardened, winged adult.
Larval flies have a variety of common names, such as wriggler and maggot.
Fly larvae have an enormous variety of feeding habits, and individual species often have very precise requirements. Many consume decaying organic matter, or are predacious, and a large proportion are parasitic on other insects and other organisms. Adult flies are almost always free-living and fly during the day. They typically consume liquid food such as nectar and other plant exudates, or often decomposing organic matter. The major morphological feature which distinguishes flies from other insects is their reduced hind wings, termed halteres.