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There are over 1000 species of native Australian snails and slugs. However, most of the snails and slugs we find in our gardens are not natives.
Most snail species arrived accidently in Australia on potted plants, or stuck to packing cases, pallets and shipping containers. A few species seem to have been deliberately smuggled in to be bred and eaten as delicacies. Unlike other exotic species, there is no evidence to suggest that these 'immigrant' snails have affected the survival of Australia's native snail fauna. In fact, most of these introduced snails invade places only after humans have destroyed the habitat of native snails.
Over 65 land and freshwater snails and slugs have been introduced to Australia from overseas. But only a few of these have become pests.
The common garden snail, Helix aspersa, has been in Australia for well over 120 years. Today, it is by far the most widespread of all our introduced species, existing in all states and territories. These snails live in non-tropical areas and avoid desert country. In Europe, predators such as thrushes and blackbirds keep Helix populations in check and cold winters limit their breeding to warmer months of the year. In Australia, warm winters allow Helix to breed for most of the year, and the lack of predators have led to it becoming a major pest.
The white Italian snail, Theba pisana, is probably the most well-known pest of Australian agricultural crops. Native to the Mediterranean, it was first found in Western Australia early this century and is now very common throughout southern Australia. It climbs the stems of cereal crops in late spring and summer and seals itself to the stems during dry spells. It is then harvested with the crop, clogging machinery and contaminating the grain. Theba can also destroy crops of dried fruit, lucerne, clover, peas, beans and oil seed.
The oriental snail, Bradybaena similaris, is native to China. It is found on the east coast of Australia, from Brisbane to Bega, and is slowly moving further south. Bradybaena is a pest of hanging fruit such as citrus.