INSECTS called backswimmers resemble humans in more ways than one. Not only do they carry their oxygen packaged up in haemoglobin as we do, but like human scuba divers they have a "buoyancy vest" which they use to regulate their depth. Other diving insects can only stay underwater by clinging to submerged objects.
Backswimmers (Anisops deanei) carry a bubble of oxygen on their abdomens that serves as their buoyancy vest. At the start of the dive, the bubble is so big that the insect floats. As oxygen is taken up by respiration, the bubble shrinks and the bug sinks as deep as a metre. When it eventually reaches neutral buoyancy, it hovers.
Philip Matthews and Roger Seymour of the University of Adelaide, Australia, measured the gas pressure inside the insect's bubble by placing a submerged backswimmer on a weight balance. To maintain depth, the insect slowly releases oxygen stored in ...
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