In Australia these have relatively short life cycles - from 10 - 40 days and most breed throughout the year. The female lays her eggs in a group as an eggstring or eggmass of up to 800 eggs (in C. duplex), either directly into water or attached to plants or stones at the water´s edge. After a couple of days the eggs hatch as larvae, which are red in colour due to the presence of numerous haemoglobins. This gives them their common name of "bloodworm". The larvae go through four instars. In the fourth instar polytene chromosomes develop in some tissues, reaching their greatest size just before the larva pupates in a silk-lined tube. After 2 or 3 days the pupa swims to the surface and the adult fly emerges. Mostly the adults live only a day or two - mating, laying their eggs and then dying. In many species the males swarm before mating, often using trees or other high objects (such as church steeples) as markers on which to orient the swarm. Large numbers can look like smoke and on occasions have led to false alarm calls for church steeples being on fire!
Some species can be readily reared or bred in the laboratory.