The first amphibious insects ever found are rare Hawaii caterpillars that can live under two feet of rushing water or on a hot dry rock and commute back and forth.

But how they breathe underwater remains a mystery.

“;They have the best of both worlds (land and water),”; says Daniel Rubinoff, an associate professor of entomology at the University of Hawaii and director of the UH Insect Museum.

When the caterpillars turn into moths, however, they leave the watery world behind for good.

Rubinoff and Patrick Schmitz, a postdoctoral researcher, discovered 12 amphibious species of caterpillars in the genus Hyposmocoma, a family of more than 400 species of moths unique to the Hawaiian archipelago.

The aquatic species are unusual because most caterpillars “;are strictly terrestrial and can't handle being underwater for any period of time,”; Rubinoff said in an interview.

“;Another highlight and surprise,”; he said, is that the caterpillars who enjoy wet or dry life “;evolved independently in the genus three or four times,”; and they are not related.

That reaffirms Hawaii as one of the world's most compelling natural laboratories for the study of evolution.

Rubinoff began observing the Hyposmocoma moths in 2002 and is continuing to learn things about them.

For instance, no moths are aquatic—even those with amphibious caterpillars, he said.

“;The adults don't spend any time underwater.”;

The amphibious caterpillars seem to like wet sunny spots where streams and rocks meet, possibly because of a buildup of algae and lichens to eat, the entomologist said.

“;They are little caterpillars that can sit on your pinkie nail,”; Rubinoff said. “;They can't run up and down rocks fast enough to escape water flow.”;

The scientists believe the caterpillars breathe through the skin of their abdomens, but they are not certain.

“;Dissection of the cases under water reveals no air bubble to mediate gas exchange, and the larvae possess no gills or plastron, common structures for underwater respiration in other insects,”; the researchers said in a paper published in the Proceedings of the National Academy of Sciences.

Developing from a larval to adult stage, the caterpillars spin silk casing around themselves representing different shapes and lineage, Rubinoff said.

The amphibious caterpillars have three different shapes, labeled burrito, bugle or cone by the researchers. Terrestrial caterpillars also have those case shapes and others, he noted.

Rubinoff said the caterpillars originally were found all across Hawaii, but their distribution has been reduced to natural flowing streams higher in the mountains. They do not exist where culverts or dikes have been installed to reroute water, he said.

“;When you look at the genetics, you would assume they are the same species, but they are very diverse—more so than we are from the chimpanzees in many cases,”; he said.

Every island has endemic species of Hyposmocoma, mostly terrestrial ones, all the way up to Laysan, Necker and Nihoa atolls, he said.

“;Each island has its own species and doesn't share that species with another island. They're incredibly restrictive. And each volcano has its own endemic species.”;

The researchers have analyzed the DNA of 89 species, and they started growing them in a trial-and-error process.

After collecting some from a rock in Manoa Stream, they learned the aquatic caterpillars need moving water to survive.

“;We put them in a tub of water,”; Rubinoff said. “;The next day they started dying.”;

He said Hawaii is “;a hot spot”; for newly discovered caterpillar species. He and Schmitz have identified 20 different case types, giving them names like “;oyster,”; “;candy wrapper”; and “;cigar case.”;

“;We're running out of names to call the different shapes of cases when we find a new species. There is an incredible diversity of case types the different species are using, and sometimes we have different species using a similar case,”; he said. “;There is an incredible amount of complexity.”;