In four to six days the tiny maggots hatch from the eggs and work their way into the leaf tissue. The larvae are full grown in seven to 16 days at which time they drop to the ground and burrow a few inches into the soil. Here each larva changes to the puparium or resting stage. Two weeks to a month later the adult flies emerge and will soon lay eggs for another brood. In central New York there are three generations and a partial fourth each year.
Winter is passed as a puparium in the soil.
Because this insect overwinters as a puparium in the soil near where the crop was infested the previous year, crop rotation should be practiced especially if one tries to mechanically protect plants from this insect. Protecting plants by covering with fine netting, cheesecloth or floating row covers will help to protect them from adult egg-laying flies. Netting will not keep out insects that are already in the soil. Be sure that the edges of the row cover are well anchored so insects cannot get under them. The protective covering should be placed over the crop at planting time and, with spinach, might be left on until ready to harvest.