Hawaiian tree snail  (Partulina physa)

Classified as Endangered (EN) on the IUCN Red List (1).

The Hawaiian Islands were once the setting for the world’s most remarkable and extensive radiation of snails, and, consequently, boast an impressive diversity of snail species (2). The Hawaiian tree snail has a flat, muscular foot that protrudes from the opening of its conical-shaped, spiral shell, and enables it to grasp firmly to trees. Typical of other snails in the Stylommatophora order, two pairs of tentacles extend conspicuously from the head, with the upper pair bearing eyes at the tip. The calcareous shell, which is lighter in weight than that of related terrestrial species, is highly variable in colour, with pigments of cream, white and brown providing an attractive, marbled appearance (3).

Historically, the Hawaiian tree snail was found across the island of Hawaii; however, today just a single relict population remains in the Kohala Mountains, with a range no more than 250 square kilometres (4) (5). 

The Hawaiian tree snail inhabits moist rainforest, approximately 1,200 metres above sea level (4).

Owing to its rarity, relatively little is known about the life history of the Hawaiian tree nail. However, as suggested by its common name, this arboreal species is found on the trunk, stem and leaves of native tree species. Moving slowly over short distances it feeds upon specific fungi, which it senses using olfactory cues (5). This species bears live young, with some four to seven offspring born per year, a slow reproduction rate amongst snails (5) (6). When born, the young measure only four to five millimetres in length, and grow slowly to reach maturity in their fourth to seventh year of age (6).  

As a result of human disturbances, the Hawaiian Islands have seen devastating extinction rates, and today, over half of the described tree snails are thought to be extinct (7). Having suffered from habitat loss, the Hawaiian tree snail is now restricted to just a single location, with a population of less than 1,000 individuals (5). This species first came under threat when the first settlers on the Hawaiian Islands began logging the lowland forests, replacing natural habitats with agricultural lands and cattle ranches. These destructive activities were compounded by the introduction of non-native predators, such as rats and the predatory snail Euglandina rosea, and alien plant species, which overgrow native plant seedlings, limiting natural forest regeneration (2). As a result, the Hawaiian tree snail, listed as a Species of Concern by the United States Fisheries and Wildlife Service, is under severe threat of extinction (8). The survival of this species is also hindered by its slow reproduction rate and the degradation of its habitat by feral pigs and goats (5) (6).  

Like many other Hawaiian snail species, the restricted geographic range and small population size of the Hawaiian tree snail makes it vulnerable to habitat degradation and, consequently, its survival may be dependant upon conservation measures (6). Fortunately for this species, efforts are underway to protect its fragile habitat. In 2003 the Ponoholo Ranch, which encompasses the Hawaiian tree snail’s habitat, entered the Kohala Watershed Partnership, which resulted in fencing being built along three sides of the ranch to exclude wild cattle, while plans were made to cull wild pigs and remove invasive weeds. The Nature Conservancy has also agreed a 15-year management plan with the ranch, with the development of a management plan for the Hawaiian tree snail a key priority (4). This vulnerable species is also benefiting from a captive breeding facility coordinated by the University of Hawaii on Lanai (5). With the successful implementation of these measures, and further efforts to remove predators and limit habitat loss, there is significant hope that the future of the Endangered Hawaiian tree snail will be secured (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the conservation of the Hawaiian tree snail, see:

• The Nature Conservancy: 
  http://www.nature.org/wherewework/northamerica/states/hawaii/press/press3850.html