Endangered Kahuli Snails on Oahu

Hail Snails!: Sometimes, you build a jail to keep bad guys out.

Vince Costello spends hours every week protecting native kahuli snails from predators.

photos: courtesy oahu army natural resources program

When the world is caving in, build a stronger cave.

That’s essentially what happened in February, when 350 endangered Oahu tree snails, known as kahuli (Achatinella mustelina), were placed inside a state-of-the-art refuge in the Central Waianae Mountain Range. The exclosure, which some are playfully calling a “snail jail,” is equipped with a fierce combination of safeguards to keep predators at bay. (Seriously, the measures make your brass deadbolt look pitiful.)

A kahuli snail.

A few years ago, biologists at the Oahu Army Natural Resources Program (OANRP) witnessed a frightening drop in the kahuli population, a species found only along the ridgeline of the Waianae Mountains. In 2004, they counted 481 snails. Five years later, more than half were gone. The culprit? Researchers saw a spike in rosy wolf snails (Euglandina rosea)—a cannibalistic snail from Florida that sucks native snails out of their shells. “We knew that if the rosy wolf snail continued, the area was going to be just another dot on the map where native snails used to be,” says Vince Costello, rare-snail conservation specialist with OANRP, a federally funded program that manages more than 100 native plant and animal species on the Big Island and Oahu.

Hawaii once had 750 species of native land snails. They were so commonly seen on trees, their nickname was “jewels of the forest.” The snails also have a place in Hawaiian culture; they’re mentioned in chants, songs and stories. Today, it’s estimated that fewer than 10 percent of the species survive. A combination of factors caused their decline, including harvesting by shell collectors, the loss of native forests and the introduction of rats and Jackson chameleons.

Snail Life

>>Kahuli snails dine on fungus. They live most of their life on leaves, even preferring particular positions, such as in a little curl of a leaf, or sandwiched between two leaves for protection.
>>At night, kahuli snails become active, even cruising from one tree to another, if the branches are connected.
>>All of Oahu’s 41 native snail species
(Achitenella) are listed as endangered, though some haven’t been seen for decades and are presumed extinct.

In February 2010, through a partnership with the University of Hawaii, U.S. Fish and Wildlife Service and OANRP, 202 kahuli snails were collected from the Waianae Mountains so that construction on the snail refuge could begin. In the meantime, the kahuli snails were taken to a snail lab at UH Manoa, for safe-keeping and potential baby-making. Home to hundreds of native snails from across Hawaii, the lab pampers each species with conditions that mimic their natural habitat. The snails even get a little spritz to imitate rain. After two years, UH biologists have successfully grown the number of kahuli snails to 350.

The exclosure has three layers of protection. For rats and chameleons, a New Zealand company, Xcluder, constructed a four-foot-high, 520-foot-long, aluminum-coated metal fence with a lip at the top. (You know, in case the animals evolve into Spiderman.) For the rosy wolf snail, an OANRP staff member invented a technique that employs rows of mesh screens. This way, the snails have nothing to grab onto. On the front line, there’s a solar-powered electric wire. If a rosy wolf snail attempts intrusion, it’s punished with a slight, nonlethal shock. Two similar exclosures are currently being built on Oahu for other native tree snails.

Since the reintroduction, Costello, who has studied Hawaiian snails for 17 years, has visited the site every week. “It’s actually very meditative,” he says, with a laugh. “Finding them is like a treasure hunt. The snails can teach you a lot of patience.”