Outside JEB iv FLIES SHORT OF BREATH

Functional interpretations of the insect tracheal system – a branched series of tubes supplying oxygen from the environment to every metabolizing tissue in the insect’s body – are plagued by two related myths. The first is that gases move through the tracheal system entirely by diffusion. This idée fixe persists despite many studies showing that, across vast taxonomic distances, insects actively ventilate the tracheal system in astonishing and subtle ways. The second myth is that the tracheal system’s direct connection between environment and tissue renders unnecessary other respiratory complications, like circulatory systems and respiratory proteins. Of course, oxygencarrying proteins (called hemocyanins) are known from insects. But their taxonomic distribution, in basal insects, reinforces the idea that advanced insects, equipped with highly evolved tracheal systems, don’t need additional help. Another class of respiratory proteins (hemoglobins) is found in a few groups of insects adapted to parasitic or aquatic habitats that expose them to hypoxia. But these were usually explained away as strange solutions to alternative lifestyles.