The exit of the tracheal system. To prevent the entrance of unwanted material the openings have a complex structure. Fly larvae have two pairs of spiracula, one pair just behind the ‘head’, another pair near the end of the abdomen. In Agromyzidae the spiracula mostly are stalked. The tracheae are connected with the outside world through three or more fine openings, each in a so-called papilla, on top of a spiraculum.
Amauromyza labiatarum: anterior and posterior spiraculum, lateral