Tropical Asia Invaded: Giant African Snail

The giant African snail Achatina fulica is typically about 7 centimetres tall, but can grow as large as 20 centimetres and weigh as much as a kilogramme. Native to East Africa, it was first introduced to Asia in 1847, when live specimens were taken from Mauritius to Calcutta, India. Today the snail is widely distributed in southern and eastern Asia, and has also invaded many of the Indo-Pacific islands, as well as the West Indies and West Africa.

Public nuisance

Away from its natural enemies, the giant African snail is able to increase rapidly in numbers, and has become a destructive pest of crops and garden plants. It also feeds on indigenous vegetation, and often poses a conservation problem by altering habitat and outcompeting other snails for food. At times it may experience population explosions and become a public nuisance, hampering human movement by covering roads and paths. In addition, the snail is a vector for disease such as eosinophilic meningitis, caused by the parasite rat lungworm that is passed to humans through eating raw or improperly cooked snails.

Although the giant African snail is a tropical species, it is capable of surviving adverse conditions – even snow – by aestivating, so it is a potential threat to countries in cooler and drier climates. While the snail has in cases been deliberately introduced for food, medicinal use or as an ornamental species, it may also be accidentally imported by the nursery and agricultural trade when soil, plants or packaging material are contaminated with the snail or its eggs. Once introduced, the eggs are typically dispersed in garden waste and in soil adhering to construction and landscaping machinery.

Control

 The snails are hermaphrodite – having both male and female sex organs – and after a single mating can lay up to 1200 eggs in a year. The effectiveness of this reproductive strategy is highlighted by a case study of the snail’s introduction and subsequent eradication from Florida in the United States. In 1966 a boy returning from Hawaii smuggled three giant African snails into Miami, and his grandmother released them into her garden. Three years later state authorities launched an eradication campaign – which ultimately cost over US$1 million – and by 1973 more than 18 000 snails had been found!

The success of the campaign can be attributed to the invader’s early detection; the giant African snail is extremely difficult to eradicate once established. Control methods include hand-collecting, poisoning with molluscicides, and even using flame-throwers! The rosy wolf snail Euglandina rosea was widely introduced as a biocontrol agent for the giant African snail, with disastrous consequences.

DID YOU KNOW?

The giant African snail is extensively farmed in Thailand and China. The canned product is exported to European markets, to meet the demand for ‘escargots’.

Reference: Sue Matthews  Tropical Asia invaded: The growing danger of invasive alien species Global Invasive Species Programme 2004