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On December 10, 2024, the Hawaii Department of Land and Natural Resources released endangered O‘ahu tree snails into an exclosure in the Honolulu Watershed Forest Service of the Ko‘olau Mountains on O‘ahu. The Achatinella fuscobasis have been extinct in the wild since 1991, and their reintroduction marks the culmination of a nearly half century of partnerships, research, and conservation work.
Read the news release from the Hawaii Department of Land and Natural Resources
Since the 1970s, the U.S. Fish and Wildlife Service has supported snail protection and recovery, especially in partnership with Hawaiʻi DLNR, the University of Hawai‘i and the U.S. Army. While conservation has been slow, it certainly hasn’t been sluggish. When it comes to saving an endangered species, even our best work may take generations.
Oʻahu Tree Snails: A Jewel of the Forest
Hawaiian kāhuli, or tree snails, have been described as jewels of the forest and have been depicted as being able to sing according to Hawaiian folklore. They have beautiful multicolored shells, and are often described in traditional Hawaiian poetry, hula, lei, and chants. Native snails also play an important role in the Hawaiian ecosystem by feeding on fungus and algae that grow on plant surfaces and by contributing to nutrient cycling in forests.
There were once more than 750 species of kāhuli in Hawaiʻi. Within the last century at least 60% of those snails have gone extinct. There are 44 Hawaiian snail species listed as endangered under the Endangered Species Act and many more unlisted species that face serious threats. Much of this extinction crisis can be attributed to non-native predators.
The Pacific rat, arrived in Hawaiʻi nearly 1,000 years ago on the canoes of Polynesian explorers. Two more types of rats, the roof rat and wharf rat, arrived from European ports hundreds of years later. As omnivores, rats consume everything from plants and seabird eggs to garbage. In the years since their introduction, rats a have become one of the most damaging invasive species in the Hawaiian islands, and have contributed to the destruction of many native plant and animal species, including snails.
In the 1930s, the giant African snail arrived in Hawaiʻi as a garden ornament. The snail is considered to be the second worst invasive species in the world, and has had a heavy impact on tropical and subtropical regions. While the giant African snail is mostly known in Hawaiʻi for being a garden pest, its presence spurred land managers to introduce the cannibalistic rosy wolfsnail to help with population control. However, in addition to preying on giant African snails, the rosy wolfsnail became terribly efficient at destroying native snail populations.
“What we found in the mountains is we’d often have a nice robust population of Hawaiian tree snails,” said Dr. Michael Hadfield, emeritus professor of biology at the University of Hawaiʻi at Mānoa. “Suddenly it would crash and what we would find is just their beautiful shells. The rosywolf snail doesn’t eat the shells, it simply shoots a big proboscis inside the shell and pulls the snail out and swallows it. Rats do crunch up the shells. So you can always tell who’s preying on who when you get there.”
(Read or listen to a full interview with Dr. Hadfield, below)
Hadfield is considered a pioneer in Hawaiian tree snail conservation, a part of the first generation of researchers who raised the alarm about the snails’ imminent extinction. In the 1970s, Hadfield and his students meticulously documented their biology, lifecycles and reproductive capabilities, and their precipitous decline. Since Hadfield started his work, rats, non-native snails, and other predators such as Jackson’s chameleons and the New Guinea flatworm have decimated native snail populations that were once abundant.
“There is no evidence that the Hawaiian tree snail had any predators during their evolutionary period,” Hadfield said. “If you read descriptions of the snails in the late 1880s or early 1900s, they talk about them hanging from the trees like clusters of grapes.”
Captive Propagation: Growing Snails in the Lab
In 1981, the U.S. Fish and Wildlife Service listed multiple species of the Oʻahu tree snail as endangered under the Endangered Species Act. Ten years later, Hadfield collected 11 of the last A. fuscobasis species of snails in the wild and began an experimental program to breed them in a lab. It was a final, high stakes effort to save this important species.
“The first one was a thing that looks exactly like your home refrigerator, except you could set day and night cycles of light inside, and also set temperature cycles,” Hadfield said. “We knew that the snails were activated by water, so we had to poke holes in the walls of our environmental chambers and plumb them so we could put in sprinklers.”
Because snails feed on molds that grow on the surface of leaves, Hadfield and his students climbed into the mountains at least every other week and brought a big bag of fresh leafy branches of ‘Ōhi‘a trees. However, instead of growing the mold directly on the leaves, they had more success cultivating the mold in petri dishes in their lab.
“You could sort of scoop it out of the petri dishes, and it would stick to the walls of the terraria and the snails ate it off,” Hadfield said. “They loved it.”
Hadfield later built exclosures, or outdoor pens, to protect snails outside in their native habitat. The first exclosure Hadfield and his colleagues built was primitive, but effective. It was an electric fence about four feet tall and 4,000 square feet, with barbed wire at the top, mostly to keep out the human type of animals. A trough of salt around the perimeter was added specifically to keep out the Rosy Wolf snail. The scientists immediately observed that the snails outside the exclosure disappeared, but the snail population inside continued to thrive.
While the exclosure program started with Hadfield and the University of Hawaiʻi, today it’s being managed by a second generation of snail conservationists and one of Hadfield’s students: David Sischo, who works for Hawaiʻi DLNR. The exclosures Sischo manages are far more advanced. Nicknamed “kāhili kīpuka” -- an homage to the Hawaiian name for small islands of vegetation surrounded by lava flow -- the exclosures are about the size of a house and have slippery, solid wall sides and electrical barriers.
“Most people imagine that the rosywolf snail is going to go flying off smoking,” Sischo said. “That’s not the case. It’s low voltage and just irritates them so they just kind of suck back into their shells and fall off the wall. It doesn’t kill them.”
Sischo intended to reintroduce the tree snails to the exclosures in late 2023, but he and his colleagues discovered that another nonnative species, Jackson’s chameleons, had infiltrated the barrier. The delay in reintroduction is emblematic of the challenges Sischo and his colleagues) are facing: without somehow neutralizing the predators on the landscape, the snails don’t have a chance of surviving in the wild.
"Conservation Needs to Happen From the Ground Up"
The ESA played a critical role in halting the kāhuli’s slide to extinction. With the listing of the snail in 1981, scientists and land managers suddenly had a means to apply for funding, mitigate threats and protect habitat. The listing of Oʻahu tree snails also meant that other species that share the same habitat could benefit from the same protections.
“We’re able to leverage the funding we get for listed species and apply it to all species that are equally imperiled,” Sischo said. “There are species that are alive today because of the Endangered Species Act.”
Sischo pointed out that the protection from the ESA isn’t enough to stave off the extinction crisis in the Hawaiian islands. For every species that receives protection under the ESA, there are many more that need protection.
“There are close to 100 snail species that may go extinct within the decade, many that we have that are already extinct in the wild, that are unlisted and not protected by the Endangered Species Act,” Sischo said. “So for the species that have been listed, it’s saved them, and for the ones that haven’t been listed, unfortunately they’ve kind of dwindled away.”
Sischo runs DLNR’s Snail Extinction Prevention Program, or SEPP, which is a partnership between Hawaiʻi DLNR, the Service, the University of Hawaiʻi, the U.S. Army Natural Resources Program, and other conservation entities and landowners. SEPP’s goal is both straightforward and herculean: to prevent the extinction of rare and endangered snails through captive breeding and wildlife management.
Joy Browning is a wildlife biologist with the Service’s Pacific Islands Fish and Wildlife Office and has helped lead snail conservation efforts. Browning said that while their urgent goal is to make sure the snails are still around in five years, they are hoping the snails will be around much longer.
“We need everyone’s kōkua (help) and ‘ike (knowledge), because no one person, group or agency has the ability, land, and tools to prevent the extinction of the kāhuli,” Browning said. “Conservation needs to happen from the ground up. It requires us to seek knowledge from around us, work with others in different roles, and rely on their strengths to help preserve what we have.
As the implementing agency for the ESA, the Service oversees snail conservation efforts. The Service provides both technical support and funding to DLNR for snail recovery, including more than $2.5 million in competitive State Wildlife Grants. Funding from the Service has helped support the captive propagation program and release of the snails into the exclosures.
“Collaboration has been the only way we’ve been able to accomplish as much as we have,” Sischo said. “The U.S. Fish and Wildlife Service has been instrumental to our efforts. They’ve gone out of their way to help us get funding and get support that we need to get these units up and get the animals into captive rearing. It’s been a great partnership and I’ve been really thankful for the U.S. Fish and Wildlife Service. The Army has been wonderful as well. They’re one of our biggest partners on O‘ahu.”
In addition to snails living in kāhuli kīpuka, snails will also be placed at the Bishop Museum in Honolulu and the Honolulu Zoo. While the goal for the next five years is to prevent extinction, there’s hope that advances in technology and predator control will allow for the reintroduction of kāhuli so the species can thrive in the wild again.
“I think the recovery of these species is not going to happen in my lifetime,” Sischo said. “It’s going to be a tag team effort. A generational effort. I think it’s going to require multiple generations of conservationists to accomplish our objectives to get these animal populations up and back out on the landscape.”
