Wednesday, May 20, 2009

O‘ahu Tree Snails - An Quick Overview

O‘ahu Tree Snails
Achatinella spp.

The entire genus Achatinella consisting of 41 species of small, colorful tree snails (Family: Achatinellidae), is endemic to O‘ahu; 22 species are believed to be extinct and 18 are near extinction. All are federally and state listed as endangered.

Check out this video from's Ecogeeks to find out more about the Oahu Tree snails, including the threat from the Rosy Wolf Snail and what's being done at UH Manoa to help establish new populations of snails:

 DISTRIBUTION: Currently, O‘ahu tree snails are restricted to remnant native forest on the highest ridges of the Ko‘olau and Wai‘anae ranges on the island of O‘ahu. Historically, the genus was widely distributed from near sea level along the windward coast to the central plains and throughout the Ko‘olau and Wai‘anae mountains.

ABUNDANCE: Unknown. However, a loss of 75 to 95 percent of native habitats supports a conclusion that the remaining populations are restricted and small.

LOCATION OF KEY HABITAT: All Achatinella snails are arboreal, which means they live in trees and bushes. Here they feed on fungi on leaves and trunks.

Although native snails are sometimes found on non-native plants, it is not known if the fungus on these introduced species is sufficient to support healthy populations. O‘ahu tree snails occur in a variety of habitats including dry, mesic, and wet forests and shrublands.
Photo: DOFAW

THREATS: Historically, the loss of native forest habitat and the introduction of rats likely affected snail populations. In the recent past, the introduction of additional rat species, over-collection, and the introduction of the carnivorous snail Euglandina rosea (Rosy Wolf snail) have resulted in declines. Ironically, E. rosea was introduced to control the giant African snail (Achatina fulica) a non-native, agricultural pest. The Giant African snail grows to be much larger than the Rosy Wolf snail.

Current threats include the continued degradation of habitat by non-native, invasive vegetation, especially strawberry guava (Psidium cattleianum), Christmas berry (Schinus terebinthifolius), and silk oak (Grevillea banksii). Pigs also degrade habitat, and predation by rats and introduced snails continues to be a problem.

CONSERVATION ACTIONS: The goals of conservation actions are not only to protect current populations and key breeding habitats, but also to establish additional populations, thereby reducing the risk of extinction. A captive breeding program at the University of Hawai‘i at Mānoa supports at least two species, A. apexfulva and A. fuscobasis, that are extinct in the wild. Watch the last section of the video above for a tour of the lab at UH Mānoa.

The above information comes from the Hawaii Comprehensive Wildlife Conservation Strategy. For more info about O‘ahu tree snails and other species of conservation need, visit the CWCS species fact sheets.

Also see the Hawaii Ecosystems At Risk (HEAR) pages for information about two native snails: Achatinella mustelina and Achatinella sowerbyana. also has info about the non-native snails mentioned above: Euglandina rosea and Achatina fulica.

Also see the US Fish and Wildlife Service's Endangered Species page for current research information. 

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