Busting an invasion myth

According to experts there are more than 12,000 non-native species in Europe, and the number is increasing. Introduced species are one of the main threats to biodiversity and are causing immense economic damage, however, not all introduced species are actually problematic. In April 2014 the EU parliament approved EU-wide measures to ban further import of non-native species and to improve the management of already established invasive species.

Spanish slugs (Arion lusitanicus) are one of the most common slug species in Central Europe. For some time conservationists have observed that the rapidly growing number of Spanish slugs is replacing the native black slug in Central Europe as well as inflicting significant damage on natural vegetation and agricultural products. Today Arion lusitanicus is the most common species of snail in Germany. It is also ranked among the "100 of the worst" invasive animal and plant species in Central Europe that are thought to have a significant negative impact on biodiversity, economy and health. The animals are sometimes nicknamed “killer slugs” because of the damage the cause in fields and gardens. Allegedly the Spanish Slug made its way to Central Europe with imports of fruit and vegetables in the 1950s.

However, researchers of the German Biodiversity and Climate Centre and the Goethe University in Frankfurt now found out, that the prime example of an invasive species is originally from Central Europe and thus no "immigrant" after all. Control measures, such as the EU regulation on prevention, early warning, rapid response, and management of invasive species which is being discussed currently, would therefore not apply to this species.

They used statistical phylogeographic techniques on the barcode region (COI) and a nuclear (nuclear zinc finger-like locus ZF) marker as well as species distribution modelling to show that the species is with very high probability not an invader, but native to Central Europe. The group led by my former Masters supervisor Markus Pfenninger also found several cryptic species in what was supposed to by one species:

Our DNA-taxonomy approach indicated the dire need of a thorough integrative taxonomic revision of the entire genus Arion. The presence of many unnamed, mostly highly divergent haplotype clades calls for thorough integrative taxonomic studies on their specific status, as several previous studies in Arion have revealed the presence of undescribed species.

Slugs already have a poor reputation because of their sliminess and their immense appetite for the veggies we cultivate. That is already unfair. They are fascinating creatures and don't deserve to be detested. At least the Spanish slug  is now cleared from the allegation of being invasive. That is a step forward.