Gill plates are located at the end of abdomens of damselfly larvae. Finally, mayfly nymph have gills on thoraces and abdomens. Just in passing, the gills of mayfly nymphs are equipped with nervous and muscular connections. The gills can be swept back and fro to mix water, and thereby alleviate the problem of local oxygen depletion. This arrangement is the source of the tracheal gill theory in arguments over the evolution of insect flight.
Gills extract oxygen from surrounding water.
Due to its low diffusion rate in water, oxygen can be depleted from water immediately local to respiratory surfaces. Moving water for this purpose is called ventilation of the gills. Some insect ventilate their gills by selecting a microhabitat where water is flowing. Still others ventilate by muscular action. This can require considerable energy expenditure because water has greater density and viscosity than does air.