Endangered Species in the Pacific Islands
O‘ahu tree snails / Achatinella spp. / Pūpū kani oe
||All 41 species of the genus Achatinella, also known as the O‘ahu tree snails, are federally listed as endangered. O‘ahu tree snails are diverse in patterns, colors, and shapes but all average about 3/4 inch in length. Most have smooth, glossy, and oblong or ovate shells with a variety of colors, including yellow, orange, red, brown, green, gray, black, and white.
|O‘ahu tree snail - Photo credit Steve Miller/USFWS
Habitat & Behavior:
O‘ahu tree snails are currently found in mountainous dry to wet forests and shrublands above 1,300 feet. They are found on trees and shrubs, are nocturnal, and feed by grazing fungus from the surface of native plant leaves. Although they are occasionally found on introduced plants, it is unknown whether the fungus of these plants provide long-term support for healthy breeding populations. Adult snails are hermaphroditic (having both male and female reproductive organs) and can live for many years. The young are born alive.
Because growth rate and fertility are very low, these snails are especially vulnerable to loss of individuals through collection, predation, or other disturbances. The most serious threats to the survival of O‘ahu tree snails are predation by the introduced carnivorous snail (Euglandina rosea), predation by rats, and loss of habitat due to the spread of nonnative vegetation into higher elevation forests.
Past & Present:
O‘ahu tree snails were once so abundant and popular on the island, they are mentioned in Hawaiian folklore and songs, and their shells were used in lei and other ornaments. Today, only 11 of the 41 species can be found.
These species occurred from near sea level along the windward coast, through the uppermost reaches of the Ko‘olau and Waianae Mountains and across the central plain.
Historically, collectors played a very large part in the decline of may of the species. Destruction of native forest habitat and the introduction of predators such as rats and alien snails are probably the major reasons for reductions in the species' range and abundance. More recently, predation by the introduced carnivorous snail Euglandina rosea and the flatform Platydemus manokwari have decimated populations of the O‘ahu tree snails.
Surveys conducted from 2005 to 2009 indicate Achatinella mustelina, a species restricted to the Waianae Range, is the most abundant of the Hawaiian tree snails. The number of snails in a single bush or tree can range from 2 to 40. Achatinella sowerbyana, from the northern Ko‘olau Mountains, is the next most abundant species with 1 to 20 snails per tree at the heart of its current range. For other species of Achatinella, usually only two or three snails are found in a single bush or tree. The number of live snails seen on any given survey range from 2 or 3 snails to more than 100. Often no snails are seen.
The entire genus of Achatinella, consisting of 41 species, was placed on the U.S. Fish and Wildlife Service Endangered Species List and the State of Hawai‘i’s Endangered Species List in 1981. The O‘ahu Tree Snails Recovery Plan by the Service and the Threatened and Endangered Species Plan for Wildlife, Plants, and Invertebrates by the Hawai‘i State Division of Forestry and Wildlife recommend improving captive propagation programs, securing essential habitat, assessing and managing current threats to the snails, continuing research, and beginning reestablishment of snail colonies.
O‘ahu tree snails can be found on protected lands managed by the State of Hawai‘i, the military, and on private lands.