Soil Dwelling Larvae
These small black flies are about 2mm long. They are often seen running over the surface of pot plants where they mate and lay up to 150 eggs into the compost. These hatch into pale coloured larvae with shiny black heads. These larvae will feed on the roots of plants, and can also tunnel into the stem of new cuttings, often killing the plants. Mushrooms are also particularly susceptible to damage from the larvae of these insects.