The larva of these flies are aquatic, rattailed maggots. The species of rattailed maggots are difficult to determine in the larval stage. The drone fly was introduced into North America sometime prior to 1874. Both flies are now common from Alaska to Labrador and south into California and Florida. They do not suck blood.
Rattailed maggots feed on decaying organic matter in stagnant water or moist excrement.
Occasionally larvae appear in alarming numbers in dung pits or animal waste lagoons. Even so, they pose little threat to man or animals. The female fly lays 4 or 5 eggs on or near contaminated water, sewage or other decaying organic matter. The larvae which hatch from these eggs are reported to reproduce paedogenetically, that is, each one gives rise to 7 to 30 daughter larvae. This method of reproduction may last for some time, but periodically female and male flies are also produced.