Amphibious Caterpillars

Underwater caterpillars don't turn into butterflies or moths, because they are dead, right? Not so for twelve species of caterpillars that live in Hawaii. Evolutionary biologist Daniel Rubinoff, who has been studying moth genus Hyposmocoma for seven years, said he couldn't believe it the first time he spotted a caterpillar living underwater.

They usually eat algae or lichen, and build silk cases -- which one species even adorns with bird feathers -- for shelter and camouflage. They spin silk drag lines to withstand the high pressure of fast floodwaters.

Unlike other amphibious creatures that can survive underwater on stored oxygen but must come back up for air, these caterpillars can spend several weeks without ever breaking the surface, according to the paper, which was published online on Monday in Proceedings of the National Academy of Sciences.

It isn't yet clear how the insects do it. Rubinoff and co-worker Patrick Schmitz of the University of Hawaii did not find any water-blocking stopper over the caterpillars' tracheae or evidence of gills. The animals drowned quickly when kept in standing water, so they seem to need the higher levels of oxygen present in running water, and probably absorb it directly through pores in their body, the scientists said.