Armadillidium /ɑːrmədᵻˈlɪdiəm/ is a genus of the small terrestrial crustacean known as the woodlouse. Armadillidium are also commonly known as pill woodlice, leg pebbles, pill bugs or roly-poly, and are often confused with pill millipedes such as Glomeris marginata. They are characterised by their ability to roll into a ball when disturbed. They typically feed on moss, algae, bark and other decaying organic matter. They are usually found in moist areas such as decomposing leaf matter and soil. Armadillidium vulgare is the most abundant species in Europe and has been introduced worldwide. However, the vast majority of species are endemic to small regions close to the Mediterranean Sea, in much lower numbers than common species such as A. vulgare, and hence are understudied.