Spanish slug – Arion vulgaris

The Spanish slug is an alien species from Europe but the exact origin is unknown. According to current knowledge, the species is originally from France and West Germany. In the latter part of the 20th century, the species has spread widely to Central and Northern Europe. In Sweden, the first observations of the species are in 1975, in Norway in 1988, in Denmark in 1991 and in Iceland in 2003.

The species is known to have locally very strong populations in Sweden, Norway and Åland. In Mainland Finland, the first observations of the Spanish slug date back to 1994. At present, the species is established in Finland up to the Oulu region, but not yet to the northernmost parts. The number of reported sightings of the species varies from year to year. The most observations have been accumulated after mild winters and during rainy and warm autumns. In Finland, in certain areas the population is already very abundant. Most sightings are reported from Southwest Finland and Uusimaa.

The eggs and young specimen of the Spanish slug are transported from one area to another with soil and with mulch surrounding the root systems of various flower or tree seedlings, bulbs and other commercial gardening products. The species can also be transported by leaf piles and compost.

Spanish slug is a hermaphrodite, i.e. one individual can act as both a female and a male at the same time. After mating both individuals can produce eggs, which is why the population can grow rapidly. In Finland, the adult slugs usually die in winter, but some of them can survive in mild winters or in favorable places. The eggs of the Spanish sliugs are very winterhardy.