A Snail’s Pace

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Story by Shannon Wianecki

Hawaiian snails
Cookeconcha hystricella lays a single, tiny, transparent egg that hatches into a baby snail. It’s unknown how many eggs this snail lays in its lifetime, or how often. Adults measure just under three millimeters. They are primarily ground dwellers. The species is one of only two survivors from the diverse Endodontidae family, which once contained 200-plus species.

Compared to most other animals in the kingdom, snails receive scant love. Humans tend to frown on slitherers, and snails not only slither, they leave trails of mucus in their wake. Sometimes they nibble on prize-winning plants. But high up in the mist-shrouded Hawaiian mountains live tiny endemic snails of a special class. Sporting beautiful shells in every shade of the rainbow, these wee creatures are worthy of our attention.

Hawaiian snails
The largest specimen on the left (Oxychilus alliarius) is an invasive species that preys upon its neighbors, two pairs of native snails from the families Endodontidae and Helicinidae.

Norine Yeung and Kenneth Hayes have devoted the last decade to studying snails in Hawai‘i. The malacologists teamed up while in grad school at the University of Hawai‘i. In 2004 they began scouring forest reserves and nurseries for foreign mollusks: invasive pests such as the giant African snail and rosy wolf snail. They collected plenty of these — but also stumbled across other species that looked suspiciously native: shy little squishes with shells shaped like cone hats or whorled discs.

“We kept finding snails that we didn’t recognize,” says Yeung. “Since we’d been told that 90 percent of the native snail fauna was extinct, we were surprised.”

Switching their focus from foreign to local, Yeung and Hayes sought answers to questions that hadn’t been asked for decades: How many native terrestrial snail species remain in the Islands? What are their relationships? What can be done to preserve them?

We knew of 750 species,” says Hayes, “but there’s a whole lot more we can’t even put names to.”

Much of what biologists know about pupu kuahiwi, or Hawaiian land snails, comes from nineteenth-century naturalists such as David Dwight Baldwin. In the late 1800s, the missionary’s son amassed 1,144 land-snail specimens from five islands. He became an authority on the subject, publishing the first scientific catalog of Hawaiian land snails. He named several species and even more were named in his honor.

The shells that Baldwin and other collectors culled from island forests are gemlike, bright daubs of colors and patterns: jade green as shiny as hard candy, yellow with mahogany and cream stripes, and fiery red with umber zigzags. They’ve lost little of their luster over the past century, and can be viewed at several local museums, including the Baldwin House and Bailey House on Maui, and the Bishop Museum on O‘ahu.

The diversity of pupu kuahiwi is astonishing; in fact, they rank among the planet’s most remarkable examples of evolutionary radiation. Scientists estimate that the Hawaiian snails’ ancestors arrived in the Islands several million years ago. Over many generations, the twenty-odd pioneer species evolved into ten unique families and as many as 1,400 species. Ninety-nine percent are endemic to Hawai‘i, found nowhere else on earth. Some species hail from a single island, even a single valley.

Hawaiian snails
Affectionately referred to as “snot in a hat,” Succinea baldwini is found on the slopes of West Maui, along with several undescribed species recently discovered by Yeung and Hayes. The pair’s work is supported by grants from the National Science Foundation (DEB-1120906) and United States Fish and Wildlife Service.

One of Yeung and Hayes’s colleagues, Marty Meyer, investigated the role that Hawaiian snails play in the ecosystem. He found that the minuscule mollusks serve a big function in the forest. They’re a food source for other native species — carnivorous caterpillars, and birds such as Hawaiian honeycreepers. More importantly, the snails help decompose and cycle nutrients back into the soil — an essential service in nutrient-poor Hawaiian forests. Unlike other snails that feed on plant tissue, pupu kuahiwigraze on the algae, bacteria, and fungi growing on the surface of leaves.

To scrape plants clean of parasitic growths, these mobile barbers use special mouth organs called radulae — something like conveyor belts punctuated by tiny teeth. Each snail species can be identified by its uniquely shaped radula, visible under electron microscope.

Now that fewer native snails inhabit the forest, hikers notice changes, says Yeung. “Old-timers say there’s a lot more fungus on trees now, so the trees are weaker.”

Of the ten native snail families,Achatinellidae is the best known. The famous O‘ahu tree snails,kahuli, belong to this family. Slow to mature, these forest jewels can reach twenty-five years of age and give live birth to one or two baby snails per year. Ancient Hawaiians prized kahuli for their beautiful shells, used in lei and referenced in folklore. An old Hawaiian chant, “Kahuli Aku,” tells of snails that chirp in the evening, asking golden plovers to fetch them water. Oral histories say these singing snails were once so abundant in the forest that they hung from trees like clusters of grapes.

Sadly, that’s no longer the case. Across Hawai‘i, pupu kuahiwi disappeared, due to loss of habitat, overharvesting by collectors, and predation by rats, Jackson’s chameleons, and rosy wolf snails.

Yeung and Hayes hope to document how many and which native snail species are left. They pay special attention to lesser-known snails, such as those in Puctidae family, nicknamed “dot snails” because they measure only one millimeter. Yeung claims a preference for anything under five millimeters in shell height. “I’m short and I’m always for the underdog,” she says. “Plus, they’re absolutely cute when you magnify them.”

Tracking down snails requires indoor and outdoor expeditions. Yeung, who works for Bishop Museum, travels worldwide to search for Hawaiian shells in the bowels of august institutions, where uncataloged specimens collect dust in drawers. “It’s like a treasure hunt,” she says. “You have to go through papers published in the late 1800s and early 1900s to see if the material you have is what you think it is. When you identify one, you’re excited.”

Searching for wild snails is even more thrilling. Yeung and Hayes catch helicopters to remote summits, rappel into plunging gulches, and camp beside pristine bogs. On the steep slopes of West Maui, they found a relatively common species, Succinea baldwini (nicknamed “snot in a hat” for its phlegm-like appearance.) They also turned up several new, undescribed species.

“Unfortunately, snails like wet weather,” says Hayes, who has hiked through many a cloudburst toting a forty-five-pound backpack and stooping every few feet to inspect leaves. Finding cryptic crawlers the size of a pinky fingernail in intermittent downpours is no easy task. The malacologists use sieves to locate small snails hiding in leaf litter, soft-touch forceps to gently handle them, and jeweler’s loupes to eye their markings.

“The shells are so small and fragile,” says Yeung. “You wouldn’t want to touch them with your fingers; you’d crush them.” The days of indiscriminate collecting are long past for these endangered species.

Conservation initiatives are under way to preserve what native snail fauna remains. The University of Hawai‘i runs a captive-breeding program and the O‘ahu Army Natural Resources Program built the world’s first snail-proof fence in the Wai‘anae Mountains to protect kahuli from predatory rosy wolf snails, plus rats and chameleons. A similar refuge is planned for West Maui.

Perhaps 90 percent of Hawaiian land snails have vanished — but no one knows for sure how many still exist. That’s why Yeung and Hayes are out combing remote Hawaiian valleys and dusty museum collections for evidence of rare pupu kuahiwi.

“We have hope there are many more out there,” says Yeung. “We just need to find them.”

Song of the Snail

Since the late eighteenth century, Hawai‘i’s land snails have fascinated European and American shell collectors — more for the beauty of their shells than as scientific specimens. After the publication of Charles Darwin’s On the Origin of Species in 1859, it became popular for many of the world’s leading scientific museums to amass and display their own collections of Hawai‘i’s intriguing land snails, whose astonishing variety provided museum visitors with a vivid example of the British scientist’s theory of natural selection.

Certain species of the Achatinellidae family are said to possess the ability to create a high-pitched whistling sound; their “songs” have also been variously described as a chirp, a trilling sound, a “cheep-cheep-cheep” or “peep-peep-peep.”

Singing snails also figure in Native Hawaiian folklore. In “Kahuli Aku,” an ancient chant put to music by the renowned Beamer family (and sung by Keola Beamer on his 2003 album Mohala Hou), a snail uses its song to ask a bird to bring it water. And in the legend of Waipi‘o Valley heroine Lauka‘ie‘ie, the singing land snail Pupukanioe offers to help her find the man she dreams of each night.

By the late nineteenth century, numerous researchers were conducting their own searches to verify or dispel the ancient stories. Many visited sites associated with the snails and confirmed they had heard the songs — but some expressed doubts about the source. In 1913, Robert Perkins, a prominent British insect expert, conducted his own investigation and found that crickets were  producing the singing attributed to the snails.

The late singer/songwriter Rev. Dennis Kamakahi touched on the controversy in his 1998 album ‘Ohana: “There’s a great scientific debate about whether it’s the land shell or the crickets you hear, but if you are from Hawai‘i, you know it’s the shell,” wrote Kamakahi in the liner notes for his song “E Pupukanioe.”—Peter von Buol


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