Since their first introduction to tropical islands in the 1800s the giant African land snails Lissachatina fulica (=Achatina fulica) and Achatina immaculata have been regarded as serious agricultural pests. These two species, originating from East Africa and Madagascar, have now been introduced to at least 27 countries, largely accidentally. Extremely high densities of these species occurred on several Pacific islands in the 1940-50s. The effects of the population explosions prompted much interest in methods of control, including hand collection, chemical and biological control. The latter has been the most widely used option. This included a variety of taxa from flatworms to reptiles, including predatory snails.
Research into molluscan predators of Achatina started in the 1940s and predatory snails started being introduced to islands in 1950 with the East African Gonaxis kibwezensis was released on Agiguan in the Marianas Islands as a test project. A survey of Agiguan in 1952 showed that the population was increasing slowly, having little effect on A. fulica. Despite the poor results of this initial project introductions of G. kibwezensis were made to 11 other islands during the 1950s. In 1957 the larger species Macrogonaxis quadrilateralis was released on Oahu and Maui (Hawaii) and later to many other islands. In 1955 the carnivorous snail Euglandina rosea was collected in Florida and released on the Hawaiian islands. 616 snails were released on Oahu island, in 1958 12,000 were moved from Oahu and transferred to other islands in the Pacific. These initial introductions were undertaken without thorough trials being completed. Although there have been some claims that this species controls Achatina there is no good evidence for this.
Other introductions have taken place:
The results of these introductions have been variable: some failed, others established but remained rare and in some places rapid expansion occurred. The established introductions did not cause the expected declines in Achatina populations and in several cases Euglandina introductions have been blamed for the rapid extinction of many native molluscs (especially in Hawaii and French Polynesia). Two families of snail have been particularly badly hit: the Partulidae and Achatinellidae. In the Partulidae sine 1978 Euglandina has been directly responsible for the complete extinction of 52 species, a further 11 survive only in captivity and another 35 are at serious risk of extinction. In the Achatinellidae the introductions in the 1950s have led to 27 complete extinctions, 27 species extinct in the wild and 22 on the edge of extinction. Many other species have probably been lost without being noticed.
In order to find ways of controlling the threat Euglandina poses to many snail faunas the ecology of the predator has been studied by several research groups, although additional studies are needed:
More details of Euglandina biology can be found on the Jacksonville shells Euglandina page
Compiled by Justin Gerlach: contact
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