"I couldn't believe it," said Daniel Rubinoff, an evolutionary biologist at the University of Hawaii at Honolulu, of the first time he spotted a submerged caterpillar. "I assumed initially they were terrestrial caterpillars... how were they holding their breath?"

In fact, the Los Angeles Times reports that 12 species of caterpillar just discovered in Hawaii are capable of spending weeks underwater without ever breaking the surface to breathe. How they do it is a complete mystery to science, but there are a few clues.

Researchers first looked at the two most likely explanations, but the caterpillars don't have gills and don't hold their breath underwater. They don't even have any kind of water-blocking stopper over their tracheae. But they did discover that the caterpillars drowned quickly when kept in standing water, indicating that the enigmatic larvae seem to require oxygen-rich running water to keep them breathing. The scientists' best guess is that they probably absorb oxygen directly through their pores, though that has yet to be confirmed.

Another unusual trait shared by these species is that they are capable of spinning silk underwater, which they usually build cases with for protection and camouflage-- one species even adorns bird feathers on its sticky casing. They also spin silk drag lines to help withstand the high pressure of fast floodwaters, a necessary adaptation since all 12 species were found in and along streams running down the mountains on several different islands of Hawaii.

While there are a number of different insect species which are capable of living underwater for long periods at a time by storing oxygen, these caterpillars are the first truly amphibious ones. After living out their larval stages underwater, they transform into moths.

Furthermore, DNA analysis revealed that the 12 species evolved their unique underwater-breathing traits independently among three lineages on different islands. Researchers noted that this is a fascinating example of how evolution works in surprising directions when members of a species become isolated from one another in remote habitats like islands.

"When the pressures on an environment are released, what crazy things are animals capable of doing?" said John W. Brown, a research entomologist with the U.S. Department of Agriculture. "You just wonder, do all animals have that potential?"