Expupated inside rearing container in which underbark frass and duff from a 2-3-year-dead pine was placed, along with larvae from that environment. I didn't see the pupa or larva when I made up the container, but this fly is pretty small and I could easily have missed seeing any. This fly was not the least bit skittish. It walked slowly and deliberately and made short flights, but never fled. If another insect approched it, it would simply sidestep the action.