How do mayfly nymphs breathe underwater?

Mayfly nymphs (sometimes called naiads) breathe underwater primarily through the use of tracheal gills. These gills are thin-walled, external protrusions of the body wall (integument) that contain networks of tracheae—the breathing tubes that form the insect respiratory system.123

These gills are typically attached to the abdominal segments of the nymph. They function by bringing the water into close contact with the closed tracheal tubes, allowing for the exchange of respiratory gases. In addition to these specialized structures, some mayfly nymphs can move their gill plates to create water currents over the exchange surfaces, which helps facilitate more efficient gas exchange. While these gills are the primary respiratory organs, considerable gas exchange also occurs across the general body surface of the nymph.13