Spanish slug – Arion vulgaris
- Invasive alien species
Government Decree on Managing the Risk Caused by Alien Species (704/2019) ? Finland’s National Strategy on Invasive Alien Species (GR 2012) ?
Kansallisesti haitalliseksi säädetty vieraslaji (Kansallinen vieraslajiluettelo)
Espanjansiruetana on säädetty kansallisesti haitalliseksi vieraslajiksi. Haitallista vieraslajia ei saa päästää ympäristöön eikä tuoda Suomeen EU:n ulkopuolelta eikä myöskään toisesta EU-maasta, pitää hallussa, kasvattaa, kuljettaa, saattaa markkinoille, välittää taikka myydä tai muuten luovuttaa.
The Spanish slug is an omnivorous colony species that has adapted to Finland’s cool climate. An individual slug may roam as far as 50 m in a night and it usually eats its own weight in food (10 g) each day.Because the Spanish slug enjoys many kinds of nutrition available in gardens, it can cause major damage in household gardens and farms. It feeds on the leaves, flowers and bulbs of ornamental and useful plants. Spanish slugs also feed on carcasses, including dead individuals of their own kind, earning them the name killer slug in the vernacular.Climate change is increasing the species’ population size in northern cultivated areas and, accordingly, the damage caused by the species, further exacerbating the danger posed to plant production.The Spanish slug may also cross-breed with other slugs, causing ecological damage to the indigenous species.Experts agree that action to combat the species is at least 10 years late, perhaps irreversibly so.
In most cases, relatively small measures are enough to prevent the slug from spreading. In the worst case scenario, however, large amounts of soil must be treated in order to eradicate the slug population.
Control measures are most effective in spring, before individuals that overwintered get to lay eggs. The slug lays about 20-30 eggs at a time and continues to do so all summer and autumn, during humid periods. Sexually mature slugs should therefore be eradicated as soon as spring comes and, in every case, before egg-laying begins.
In home gardens, Spanish slugs should be collected and killed by decapitation or immersion in boiling water. Efficiency of collection can be enhanced by placing boards on the ground to collect moisture, as this will attract the slugs. The dead slugs should be placed in a closed waste container or buried in the ground, so that they do not provide nutrition for other slugs.If the slugs cause damage in large areas, the contaminated soil must be removed to a depth of 10 cm. The removed soil should then be placed in a pit in the ground or stacked in heaps. The pit and heaps of soil should then be covered with a thick layer of soil. A layer of 0.5 metres is probably sufficient. If compacted, the covering layer is more effective. Such a thick and compact layer of soil will prevent the developing slugs from accessing the surface.
What can I do?
If Spanish slugs are found in the area, you should keep the lawn and all vegetation in the garden low and neat. This will prevent the slugs from finding shelter from desiccation. Heaps of leaves and twigs should be burned to destroy the slugs’ overwintering locations. Liming of composts is another method of controlling slugs.No soil, leaves, compost or plants may be transferred from areas where slugs are present. This will prevent the slugs and their eggs from being transferred to new areas.Lime sprinkled on the compost will absorb the water from the slugs. Liming should only be performed to control Spanish slugs, as lime affects the micro-organisms in compost. Open composts must be avoided.