Non-native land snail species are increasing exponentially

To date, there has been a lack of information on the spread of alien species, particularly invertebrates such as snails. "Despite efforts to compile lists of alien species, there is not even a well-documented list of alien invertebrate species for Europe," emphasises Prof. Dr Bernhard Hausdorf, Head of the Mollusca Section at the LIB. His study, which has just been published in the journal NEOBIOTA, provides a basis for decisions on further measures to control or eradicate introduced populations.

Land snails play a key role in ecosystems. For example, they decompose decaying plants and thus play an important role in the nutrient cycle and in soil formation. However, more and more species are being spread beyond their native range, usually by humans, sometimes intentionally, but often also unintentionally through trade or travellers.

The study analyses 22 species of land snails that have been introduced to Europe and the Mediterranean region from other continents. Most of them are small, live on decaying plant parts and apparently cause hardly any problems. However, carnivorous species can threaten native snails, and species that feed on vegetables and lettuce can cause damage to agriculture. Some species even serve as hosts and vectors of parasites that can cause, for example, encephalitis and thus indirectly harm human health.

Harmful species include the Laevicaulis species recently introduced to the Mediterranean region from tropical Africa and the African giant snail Lissachatina fulica. They can cause economic damage on irrigated agricultural land or in greenhouses by destroying or contaminating crops so that they can no longer be sold.

In his study, Bernhard Hausdorf analyses records of land snail species that were introduced into the Western Palaearctic region, Europe and the Mediterranean from other regions after 1492 and have become established in the wild. He observes that the number of alien species has increased continuously since the 19th century, even exponentially from the 1970s onwards, and that the introduced species have continued to spread.

Within Europe, alien species generally colonise from south to north and from west to east. Thirteen of the 22 species analysed came from North America, three from sub-Saharan Africa, two from the Australian region, three probably from the Oriental region and one from South America.

Even if trade relations and the preparation of species can be correlated, Hausdorf believes that the prevailing climate is primarily decisive: "The spread of many of the introduced species, especially the tropical species spreading in the Mediterranean region, is probably favoured by climate change."