Scientists discover world's first amphibious insects: Hawaiian caterpillars

Jeremy Hance
March 22, 2010

Scientists have never before discovered a truly amphibious insect until now: writing in the Proceedings of the National Academy of Sciences researchers have announced the discovery of 4 species of Hyposmocoma moths in the Hawaiian islands which they consider truly amphibious—that is a species able to survive both on land and underwater indefinitely. Hyposmocoma moths are native only to the Hawaiian islands and comprise over 350 species.

When the amphibious moths are in larva form, as caterpillars, they "can breathe and feed indefinitely both above and below the water’s surface and can mature completely submerged or dry," the researchers write. They add that since the larvae inhabit fast-flowing streams where floods are common, they have evolved remarkable skills to "withstand extremely high and fast floodwaters, which can scour the rainforest streambeds for days during frequent storm events. Through a combination of specialized shelter-seeking behavior and use of silk tie-downs and drag lines, larvae avoid exposure to the strongest currents."

The caterpillars are also notable for the feeding habitats: they are the first caterpillars known to eat snails and mollusks, which they bind with their silk.

The researchers speculate that since the caterpillars have no gills or plastron, they "likely rely on direct diffusion of oxygen through the hydrophilic skin". This would explain why the caterpillars only occur along fast-flowing steams and why they perish in stagnant water.

As strange as these amphibious evolutionary adaptations appear, the researchers believe that these four moths evolved amphibious traits not once, but several times in a phenomenon known as 'parallel evolution' where different species evolve similar traits separately.

"Similar patterns of parallel evolution in which related taxa independently derive similar ecologies has also been found in Hawaiian birds and damselflies," the researchers say. In addition, a lack of aquatic insects on the Hawaiian Islands may have provided an open niche for the caterpillars to take advantage of.

The moths are in need of active conservation measures according to the researchers, since they are threatened by habitat loss due to streams being diverted for culverts and dikes. At one time there may have been more amphibious caterpillars but the paper concludes that they "may already be extinct" due to habitat destruction.

Per square mile the Hawaiian Islands have more recognized endangered species than any other place in the world, hence its nickname: Endangered Species Capital of the World. Hundreds of species have already vanished from Hawaii since Europeans first arrived in the late 18th Century; several more species are known to have disappeared when the Polynesians first arrived.

CITATION: Daniel Rubinoff and Patrick Schmitz. "Multiple aquatic invasions by an endemic, terrestrial Hawaiian moth radiation." PNAS.

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Jeremy Hance (March 22, 2010).

Scientists discover world's first amphibious insects: Hawaiian caterpillars.