Tandonia sowerbii

Tandonia sowerbii, commonly known as the Sowerby's slug or keeled slug, belongs to the family Milacidae. This gastropod mollusk is a significant agricultural and horticultural pest. It is distinguished by a prominent keel running along the back and its exceptional ability to burrow deep into the soil, which helps the species survive drought and cold weather, making it particularly difficult to eradicate.

The diet of this slug is highly varied, causing damage to a wide range of vegetable and ornamental crops. It shows a strong preference for root vegetables such as potatoes, carrots, and parsnips, often feeding from below the soil surface. Furthermore, it aggressively attacks seedling beds, lettuce, brassicas, and various strawberry cultivars, often consuming entire plants during their most vulnerable growth stages.

The biological cycle of Tandonia sowerbii is heavily influenced by soil moisture and temperature. These slugs are nocturnal, preferring to spend daylight hours in deep soil fissures or beneath debris. They are hermaphroditic and lay clutches of eggs in damp, protected areas. With multiple generations possible in favorable climates, populations can explode rapidly, especially in gardens with heavy, damp soil and high organic matter content.

Damage caused by this pest is characterized by deep, unsightly cavities in tubers and roots, which renders them unmarketable. On leafy crops, the slugs create large, ragged holes, often leading to the complete skeletonization of the plant. Moreover, their slime trails and feeding activity provide pathways for secondary fungal and bacterial infections, leading to the rapid deterioration of harvested or growing produce.

Effective management of Tandonia sowerbii relies on an integrated approach focusing on habitat modification and direct control. Key strategies include:

• Cultivating the soil to destroy burrows and expose eggs to predators.
• Removing debris, weeds, and hiding spots that provide shelter for the slugs.
• Using barrier materials like copper tape or sharp grit around sensitive plants.
• Application of molluscicides, preferably those based on iron phosphate, which are safer for hedgehogs and domestic pets compared to metaldehyde.