Larvae breathe through spiracles located on their eighth abdominal segments, or through a siphon, so must come to the surface frequently. Source: Internet
The bubble covers at least some of the spiracles, thereby permitting the oxygen to enter the tracheae. Source: Internet
The distribution of spiracles can vary greatly among the many orders of insects, but in general each segment of the body can have only one pair of spiracles, each of which connects to an atrium and has a relatively large tracheal tube behind it. Source: Internet
The front eight segments have spiracles and the terminal segment is modified for reproduction. Source: Internet
The front two segments have a pair of spiracles which are used in respiration. Source: Internet
The physical properties of the interface between the trapped air film and surrounding water allow gas exchange through the spiracles, almost as if the insect were in atmospheric air. Source: Internet