Black Slug - Behaviour

Behaviour

The black slug is mainly nocturnal and avoids exposure to sunlight. It is omnivorous, eating carrion, fungi, and vegetation (living and decaying). The slug prefers moist conditions, such as lawns, making it an unwelcome sight for homeowners. This moist environment is essential for the terrestrial locomotion of the slug to function.

Like all other species of the Arionidae family, the black slug is a hermaphrodite, meaning it can fertilize itself if needed, although a mate is preferred. After mating, the slug lays eggs about 5 mm in diameter. The favoured location for eggs is a dark, cold, damp place such as a compost heap.

In the past two decades, its mating with the non-native (at northern latitudes) pest species Arion vulgaris (or Spanish slug) has resulted in a more resilient hybrid exhibiting increased tolerance to cold.

The mucus of the slug is highly distasteful to many animals. However, this slug does have some natural predators, including the hedgehog, badger, shrew, mole, mouse, frog, toad, snake, carnivorous beetle, and some birds. When picked up or touched, the black slug will contract to a hemispherical shape and begin to rock from side to side. This defensive behaviour confuses predators, and is unique in the Arionidae family.