The air-vent, or snorkel, enabled U-boats to remain operational yet relatively safe from the watchful eyes of Allied destroyers. Ingenious though it was, it was scarcely new, not by a million years or so. The water scorpion is one of several insects that make use of a similar device and for similar reasons - to be both operational and invisible. Its long tail, which gives it a passing resemblance to the land scorpion, is in fact a breathing tube that the creature thrusts above the surface of a pond edge or ditch while its front end clings to a weed stalk under water, wathing for prey.
An even more advanced adaptation has been made by rat-tailed maggots, the larvae of drone flies that live in ponds. The maggot can extend its tail upwards as much as 6 in (15 cm) to reach the surface. It is a true snorkel in that it supplies oxygen to gills in the maggot's rear end.