Four Finnish cities have launched an unusual campaign to tackle the growing threat of the Spanish slug (Arion vulgaris), a highly invasive species considered one of the most destructive garden pests in Europe. Locals in Lappeenranta, Turku, Kerava and Jämsä can now earn 6 euros per litre of dead slugs they collect, as part of a summer initiative to reduce the pest’s rapidly expanding population.
Invasive Spanish slugs thrive in wet Finnish summers
The Spanish slug has adapted well to the humid summers of southern and central Finland, where it can grow up to 14 centimetres and lay hundreds of eggs per season. Nicknamed the “killer slug” for its aggressive feeding habits and reports of preying on bird chicks, the species has been spreading steadily across Finnish gardens and green spaces.
According to city gardener Maisa Hautala in Lappeenranta, the situation became critical last summer. “We received an overwhelming number of reports about Spanish slugs,” she explained. In response, the city began distributing slug poison free of charge to residents and joined the collective reward programme.
Crowdsorsa app rewards slug hunters
Residents participating in the campaign are encouraged to use the Crowdsorsa app, a Finnish digital platform designed to crowdsource environmental tasks. Originally used to control other invasive species like lupines and Himalayan balsam, the app now allows users to earn money by uploading videos of slug disposal procedures.
To qualify for the six-euro reward per litre, participants must collect the slugs in sealed one-litre containers, record the packing and disposal process, and submit the video via the app. Each city has allocated 1,750 euros (approx. €1,850) to finance the slug bounty.
Ethical and practical challenges
Despite the financial incentive, participation has been lower than expected. Crowdsorsa CEO Toni Paju noted that many people find slug hunting physically unpleasant and ethically questionable. “Killing slugs is more unpleasant and requires more effort than, say, cutting down a lupine,” he said.
There are also practical concerns. The Spanish slug closely resembles the native ash-black slug (Limax cinereoniger), which is harmless and should not be targeted. Furthermore, handling slugs without gloves poses a health risk, as they can carry harmful bacteria like listeria and E. coli.
The recommended disposal methods include cutting the slug between its tentacles, crushing its head with a rock, or pouring boiling water over it in a container—a method preferred by many families due to hygiene and discomfort concerns.
A broader invasive species strategy
The initiative is part of Finland’s broader strategy to manage non-native species that threaten local biodiversity. While the slug bounty may appear unusual, it reflects the country’s growing reliance on community-based responses to environmental threats. With wet summers expected to become more frequent due to climate change, managing the population of invasive slugs could become an annual challenge for municipalities.
