Giant African Snail
Image of four Giant African Snails on a tree (Photo from: www.bugwood.org Credit to: David G. Robinson)
- Adults usually around 7-8 cm tall, but may reach 20 cm or more
- Shell has rounded conical shape, being about twice as high as it is broad
- Shell is generally brown in color with irregular darker streaks running transversely across the whorls
- Adult size is reached in 4 months, but may continue slowly up to 1 ½ years
- Cross-fertilizing, egg-laying hermaphrodite
- Number of eggs per clutch averages around 200 with 5-6 clutches per year
- Hatching viability is about 90%
The Giant African snail, Achatina fulica, has been widely introduced to Asia, to Pacific and Indian Oceans islands, and to the West Indies. It has also been intercepted widely by quarantine officials and incipient invasions have been eradicated, for instance in the mainland USA. The Giant African Snail is also a vector (as are many snail species) of several human pathogens and parasites. Often its introduction leads to the subsequent introduction of predatory snails and, more recently, flatworms as putative biological control agents that can have devastating effects on native land snail diversity.
The Giant African Snail has been widely introduced throughout the tropics and subtropics. After introduction, its populations generally increase dramatically, perhaps following a variable lag time, as seen in many other introductions of non-native species. The snails frequently reach such enormous numbers, at least locally, that they become not only agricultural and garden pests but also a major public nuisance, causing road hazards and making it difficult to avoid them while walking.
The Giant African Snail has been considered the most important snail pest in the tropics and subtropics and perhaps the world. However, its agricultural impacts may have been exaggerated, the nuisance factor perhaps being more important. By reaching such enormous numbers and invading native ecosystems they also pose a serious conservation problem. Not only may they eat native plants, modifying habitat, but they probably also out-compete native snails. The Giant African Snail is also a vector of Angiostrongylus cantonensis (Nematoda; Protostrongylidae), the roundworm responsible for eosinophilic meningo-encephalitis in humans and the spread of the disease has been correlated with the spread of Giant African Snails. However, many other introduced snails in the tropics are vectors of this parasite and the spread of the disease has not definitively been related to the spread of Giant African Snails.
Invasion Pathways to New Locations
Giant African Snails are introduced to new locations in various ways. Sometimes, they are accidentally imported, probably as eggs or small snails, with agricultural products. Also, the snails are deliberately introduced to new environments as a novelty pet. They are even smuggled as food, medicinal use, or ornamental. Furthermore, Giant African Snails are brought in accidentally with plants and soil when they are either eggs or small individuals. On occasion, some snails may get attached to vehicles unobserved or attach to sea freight containers or their contents.
Local Dispersal Methods
Locally, the eggs and snails are readily transported in garden waste. Occasionally, the Giant African Snail may get attached to machinery (e.g., road construction, landscaping) unobserved.
Portions of this article courtesy of: Global Invasive Species Database