The adult bean fly is a small, shiny, metallic black fly about 2 mm in length. Adult female bean flies deposit their eggs on or in recently unfolded trifoliate leaves or in the developing stems. Within two to four days the eggs hatch into yellowish white larvae, which tunnels into the leaf tissue. The larvae grow, molt and burrow into the stem of the host plant over a period of 8 to 10 days, and then turn into a barrel-shaped pupae below the stem surface. After 7 to 9 days, the adult fly emerges from the pupae and the cycle is repeated.