Hermaphrodite Spanish slugs – or Arion vulgaris – have caused major damage to gardens and crops in Riihimäki in the past, and the authorities say they are poised to start fighting off the alien species as soon as spring begins this year.
The gastropod is considered among the 100 worst alien invasive species in Europe according to the EC-funded DAISIE project. It's the continent’s worst slug pest, with important economical, ecological, health and social impact.
The most effective way to combat the slugs is the tried and tested method of picking them up and collecting them – preferably before they begin to lay eggs, which they do in their hundreds. Because the species is a hermaphrodite and able to reproduce asexually, a single slug is enough to start an infestation.
Keeping green areas well trimmed also prevents the slugs spreading.
Last spring Riihimäki authorities were forced to dispatch streetcleaning lorries to collect the slugs, and spent around 30,000 euros on containing the outbreak.
The Spanish slug made its first recorded appearance in Finland in 1990. According to the DAISIE project, Arion vulgaris causes severe damage to horticultural plants in private and public gardens and cultivated crops in agriculture.