Impact of Invasions
In addition to the direct negative effect of Theba pisana feeding on agricultural crops, it also has several other additional effects. It uses the stalks of cereals as aestivating sites, which in turn clogs machinery and fouls produce during mechanical harvesting.
According to Quick (1952) Theba pisana has been responsible for the extermination of native snail species as a result of competition for available food.
In their report on the status and potential impacts of alien invasive organisms in the fynbos biome, MacDonald & Jarman (1984) predicted that Theba pisana would have very little impact on ecosystem processes, such as nutrient cycling, energy flow and sediment dynamics or on the germination and succession processes of the plant community itself. However, the snail could seriously impact directly on fynbos plants, by feeding on them, and also displace native herbivores by competing with them for resources, and these effects have not been studied.
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