The Danish Society for Nature Conservation has urged authorities to take on the Spanish slug, citing that the species is not indigenous to Denmark and should be eradicated.

Related to the black slug, the Spanish slug that hails from the Iberian peninsula has few enemies in the Nordic countries.

The species is believed to have arrived about 20 years ago, likely with plant shipments, and has since spread, related to the black slug.

A relatively warm and wet spring season this year has provided ideal circumstances for the slugs, one that has lead them to become a plague.

Dubbed the ‘killer slug’ because it eats dead members of the same species, the slug can grow to about 12 to 15 centimetres in length and has become a pest for many homeowners, but has also spread to parks, recreational areas and farms.

Experts estimate that a single slug, which is a hermaphrodite , can lay about 400 eggs, and start an infestation.

“When an animal eats the killer slug it gets its mouth full of thick slime and spits it out again,” reports Ted von Proschwitz of the Gothenburg Natural History Museum.

Now, homeowners in Sweden have begun to smuggle-in pesticides from neighbouring Denmark and Germany in an attempt to eradicate the slugs.

Beer also seems to attract the slugs, Von Proschwitz said. There are, however, risks with trying to poison the slugs, as other slugs, snails and frogs risked being killed.

Newspapers and authorities are offering tips on how to protect land, including not having open compost heaps.