Photo: Steve Nanz
Ants have nests that they defend and use for storage of food. Other animals, (inquilines) can associate with ant nests and find protection. Inquilines must avoid attack by ants, either by chemical defense or by mimicry of the nest odor of the ants. The ant woodlouse, feeds on ant droppings. This activity benefits ants. by keeping the nest more sanitary. The ant woodlouse is only found underground in ant nests.
Source: Living With Insects Blog