The adults with their characteristic dancing flight do not bite. They only ingest liquids and live only long enough to mate and produce eggs. They die after about five days.
The use of cedar wood chips is one way to keep Sciaridae away from plants.
As a pest of plants, sciarid larvae feed on the root system. In both industries, adult sciarid flies are a nuisance pest that can result in crop rejection if high numbers are present in the growing area.
The damaging larval stage can be controlled using the beneficial nematode Steinernema feltiae, which enters the larva and releases a bacterium that kills the insect. The nematode then reproduces within the larva and its young are released into the growing medium, where they actively search out new host larvae.
Edit: Ha! Ha I also think that the spots are from lack of calcium.