Arion

Description

The Spanish slug is a culture-linked invasive alien species from Southern Europe. At the late 20th century, it has spread unintentionally with human to a wide area in Central and Northern Europe. The colour of the Spanish slug varies and it is tall, as full-grown about 7 to 14 cm long. The omnivorous species has adapted well to the cool climate in Finland.

Distribution in Finland

Manner-Suomessa ensimmäiset havainnot ovat vuodelta 1994. Nykyisellään laji on vakiintunut Suomeen pohjoisinta osaa lukuun ottamatta. Lajin havaintoilmoitusmäärät vaihtelevat vuosittain. Havaintoja on kertynyt eniten leutojen talvien jälkeen sekä sateisina ja lämpiminä syksyinä. Suomessa on tiettyjä alueita, joilla kanta on jo erittäin runsas. Eniten havaintoilmoituksia on Varsinais-Suomesta ja Uudeltamaalta.

Identification

Newly hatched Spanish slugs are approximately one centimetre long and they grow up to 7–14 cm in length. The colour varies greatly. In Finland, individuals are usually dirty orange-reddish-brown, dirty brown or black. Young individuals may also have dark longitudinal lines on the sides. In a Spanish slug, the spiracle on the right side is located at the front of the central part of the shield. The back is convex, it doesn't have a ridge and, when looking from above, the rear part is rounded. The underside is completely white or the edges may be slightly darker. The mucus is almost colorless. Spanish slugs usually occur in large numbers so when you find one, most likely there are others nearby.

Spanish slug should not be confused with the large, often almost black or black and white striped, sometimes grey ash-black slug (Limax cinereoniger) the underside of which is white with sharp bordered black edges. The ash-grey slug is a native species in Finland and there is no reason to eradicate it. Due to the large variation of the colour of both species, it can be difficult to distinguish between species. However, they can be distinguished by the location of the spiracle which is located on the ash-grey slugs on the back of the central part of the shield. In addition, an ash-grey slug has a longitudinal ridge on its back which continues up to the sharp tip of the back. On the Spanish slugs the ridge is missing and their back is evenly convex. Also, the ash-grey slug never appears en masse, but usually singly.

The young orange-brown Spanish slugs with dark longitudinal lines on the sides may resemble the most common slug in Finland, the dusky arion (Arion fuscus). Even the largest dusky arions remains about 7 cm long, and their mucus is orange. Dusky arions' main habitat is a forest, although they also live in yards and parks, but not en masse like Spanish slugs.

Compare the Spanish slug to the ash-grey slug and the dusky arion in Pinkka -online learning environment (change language on the top) on the identification of alien species.