The collapse is delayed because nitrogen moves into water only slowly, but sooner or later, air bubbles will collapse. Insect using air bubbles as physical gills must return to the surface. If an air bubble were non-collapsible, many aquatic insects would not have to surface. Some insects, such as the water bug Apohelocheirus are equipped with a plastron, which holds a non-collapsible thin film of air along the outer surface of the body. A plastron is continuous with the trachael system.
Plastrons typically run along the body surface, continuous with the spiracles.
There are cuticular openings which lead into air channels, which in turn lead to spiracles and trachael systems. The hydrophobic quality of hairs along the air channels serve to keep water out of trachael systems. The most efficient arrangement of plastron hairs would be to have them parallel to a body surface. Insects approximate this by having the tips of plastron hairs bent, or else they slope as some angle, so that air films resist collapse when subjected to higher pressures. Plastrons function in the same patterns as air bubbles when they are extracting oxygen from water, that is to say, they act as physical gills.