Pacific Tree SnailsPartulidae Pilsbry, 1900 |
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 Partula radiolata from the Island of Guam. Photo: Alfred Daniel J. (iNaturalist). |
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 Samoana conica from American Samoa. Photo: Ben Hayden (iNaturalist). |
For biologists, isolated ecosystems are of particular interest: Island or other areas that are not connected to a larger landmass. By this isolation, species evolved that are found nowhere else on Earth: Endemic species. A very large, isolated region is the continent of Australia, which has separated early in Earth's history from Asia and Antarctica. There, primordial groups like the marsupials (Marsupialia) and monotremes (Monotremata) were able to evolve in great diversity, while they are all but extinct on most other continents.
Many islands far enough away from continental landmasses, also are home to endemic species of animals and plants. Among the gastropods, well known examples are the genera Liguus from the Caribbean, Achatinella from Hawaii, as well as the genera Partula and Samoana from Polynesia (both of which are part of the Partulidae family), and last, but not least, the Cuban Tree Snails (Polymita picta), only present in the eastern part of Cuba.
 Partula lutaensis from Rota, Northern Mariana Islands. Photo: Rachael Kaiser (iNaturalist). |
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Partula snails are found in French Polynesia, the Palau Archipelago and the Mariana Islands. Their shells usually are not longer than 2 cm: In comparison they are about as big as the egg of a Giant African Land Snail (Lissachatina fulica).
There are over a hundred species of arboreal Partula snails, living in wooded habitats on tree trunks. Juveniles are rather found in the lower parts of the trees, older specimens often climb higher on the tree. The life expectancy of those snails is estimated to be about five years.
A biological peculiarity: Partula snails are ovoviviparous, they give birth to living young, a means of reproduction rare in snails, but also seen, for example, in some species of European door snails (Clausiliidae).
The story of the Polynesian Tree Snails is an example for the vulnerability of such isolated ecosystems. With the arrival of humans on those islands, so did non -domestic animals, such as pigs, cats and dogs, as well as cultivated plants, which changed the countryside and its vegetation, as well as the habitats therein.
On the island of Moorea (Society Islands, French Polynesia
Map) the disappearance of Partula snails began in the 1960s, when
Giant African Land Snails (Lissachatina
fulica) were introduced, originally to be cultivated. The project was a
failure, and the snails were released into the wild. Thanks to their
adaptability, they spread out, some even to other islands in the vicinity. By
nutritional competition, the harmed the noticeably smaller species of domestic
tree snail species.
 Euglandina feeding on a Bradybaena similaris. Photo: Bill Frank, Jacksonville Shell Club. |
To get rid of the problem, without considering the possible ecological consequences, a predator snail was subsequently introduced: The Rosy Wolf Snail (Euglandina rosea). This specialised snail hunter hunts other snails along following their slime thread, climbs trees and even can pass narrow waterways. However, instead of decimating the large African Land Snails, which they absolutely can do, Euglandina rosea preferably hunted the smaller domestic Partula species. Those were entirely defenceless against the new predators.
Apart from Euglandina rosea, two predator snail species from Africa were also introduced to other Pacific islands: Tayloria (formerly Gonaxis) quadrilateralis and Tayloria kibweziensis from the Streptaxidae family. Those are also referred to as "hunter snails". Like the Rosy Wolf Snail before, those also preferably hunted the small domestic snail species instead of the giant African species.
Herbert,
D., Kilburn, D.: "Field guide to the Land
Snails and Slugs of Eastern South Africa", Natal Museum Pietermaritzburg, 2004.
S. 151 ff.
However, not only predator snails were introduced: To fight the African Land Snail plague, from New Guinea, a predatory terrestrial flatworm, Platydemus manokwari was introduced. Those not only infected the African land snails, but also the small endemic tree snails, to which they did decidedly more harm, since those are noticeably rarer.
 Partula
Snail: RZSS Conservation Projects - Great days out for a good cause!YouTube Video on the Edinborough Zoo channel. |
In 1983 already, Tillier & Clarke (see below) had estimated that at least one hundred endemic snail species had gone extinct already and several hundreds more were threatened and would follow.
Internation conservation projects were able to collect species in time to take them into zoos and research institutions, among those the Durrell Zoo (Jersey), the Shedd Aquarium (Chicago) and the London Zoo. Partula snails are very demanding in captivity: Temperature, humidity, light and food must be exactly right, otherwise the snails will not reproduce. Nevertheless, some colonies were able to be preserved that way.
Some attempts have been made to re-introduce species into the wild. A special success was achieved in Aril 2010 by the zoo of Bristol: Partula faba from Raiatea Island, extinct in the wild, had 15 living juveniles hatched.
There were, however, also setbacks: In 1993, the London Zoo managed to achieve a population of 400 Partula turgida. Those were released into a fenced enclosure on the island of Moorea. However, by 1995, this population had be decimated by wolf snails to such an extent that it was not able to survive. The specimens remaining in the London Zoo then died out because of an infection by the parasite Steinhausia. According to Ferber (1998), this was the first documented case of an entire species obliterated by an infectious disease.
Latest Change: 25.10.2026 (Robert Nordsieck).
