The body length of the adult slug is 100 to 130 mm. The shell is fairly large and narrow, up to 13 mm in length and 7 mm wide. The body is slender, narrowing towards the tail. The animal's body colour is pale-grey, ash-coloured, brownish or sometimes yellowish-white. The body is longitudinally streaked or spotted with black. The shield is black-spotted. The tentacles are pinkish-brown, with no dark speckles. The sole of the foot light-coloured, and the colour is always uniform. The mucus is colourless and iridescent.
Near human habitation, slugs are commonly found in lawns, gardens, greenhouses, cellars, tunnels and underground canals. Their can be seen hiding under bits of timber, in tree hollows and bark, and under rocks. In the wild, the species are restricted to deciduous and mixed forests. The great grey slug is common throughout Europe, except the far north.
They thrive in damp areas and places with above-zero winter temperatures. The animal feeds on fruit and vegetables, with preference for fallen and spoilt fruit.