found this newly emerged adult which will get darker with time.! the projection seen on the front of its head (pics 1, 2, 3) is the "ptilinum"... an eversible bladder-like pouch just above the base of the antennae... and body fluid is pumped into its head to inflate the ptilinum.! it is used to force off the end (cap) of the puparium in order for the adult fly to emerge... and after this inflation at emergence... the ptilinum collapses back inside the head... marked thereafter only by the ptilinal suture or frontal suture.!