Laevicaulis alte is a round, dark-coloured slug with no shell, 7 or 8 cm (2.8 or 3.1 in) long.

The tentacles are small, 2 or 3 mm (0.079 or 0.118 in) long, and they are only rarely extended beyond the edge of the mantle.

This slug is an intermediate host for Angiostrongylus cantonensis, the rat lungworm, a round worm, the most common cause of eosinophilic meningoencephalitis.

Laevicaulis alte has several adaptations for living in dry conditions: a rounded shape with as small as possible surface area, and a narrow foot to reduce evaporation.

Juvenile specimens search for food nearly always at night, and stay buried in the soil during the day.