Spanish slug

Systematic position. The Spanish slug (Arion lusitanicus) is a gastropod mollusk belonging to the family Arionidae. As an invasive species, it has become a major agricultural threat, often outcompeting local fauna and rapidly spreading across various temperate climates due to its high reproductive rate and lack of natural predators.

Crops damaged. This pest is highly polyphagous and feeds on a wide range of plants. Major targets include horticultural crops such as lettuce, cabbage, broccoli, strawberries, and potatoes. Furthermore, they are notorious for destroying seedlings in early spring and consuming ornamental plants, causing significant economic losses for both home gardeners and commercial farmers.

Biology and life cycle. Spanish slugs are hermaphroditic and highly prolific, with a single individual capable of laying hundreds of eggs in damp soil during the growing season. Their life cycle is closely linked to moisture levels. They hide in soil crevices or under garden debris during dry periods and emerge in large numbers during wet weather to feed and mate, ensuring their survival across seasons.

Damage and harmfulness. The feeding habits of Arion lusitanicus are characterized by the consumption of large, irregular holes in leaves, stems, and fruits. Beyond direct consumption, they reduce the quality of produce through the secretion of sticky mucus and by acting as vectors for various plant pathogens. A heavy infestation can effectively defoliate entire rows of crops in just a few days.

Control measures. Effective management strategies include a combination of mechanical, biological, and chemical interventions:

• Hand-picking slugs during evening hours or early mornings.
• Installing physical barriers such as copper tape, grit, or crushed eggshells.
• Using beer traps or commercial baits based on ferric phosphate.
• Implementing biological control using parasitic nematodes (Phasmarhabditis hermaphrodita).
• Reducing shelter spots by clearing garden waste, weeds, and dense vegetation.