|Armadillidium vulgare in its defensive posture|
Armadillidiidae is a family of woodlice, a terrestrial crustacean group in the order Isopoda. Unlike members of other woodlouse families, members of this family can roll into a ball, an ability they share with the outwardly similar but unrelated pill millipedes and other animals. It is this ability which gives woodlice in this family their common name of pill bugs or roly polies. The best known species in the family is Armadillidium vulgare, the common pill bug.
Ecology and behaviour
Woodlice in the family Armadillidiidae are able to form their bodies into a ball shape, in a process known as conglobation. This behaviour is shared with pill millipedes (which are often confused with pill bugs), armadillos and cuckoo wasps. It may be triggered by stimuli such as vibrations or pressure, and is a key defence against predation; it may also reduce respiratory water losses.
Relationships with people
Pill-bugs can be considered pests of homes and gardens. They are, however, cherished among children, who enjoy keeping them as pets.  Keeping a pet pill bug requires a very moist habitat with limited light. They can live for about two to three years.
Owners of pet tarantulas sometimes keep pill bugs as cage cleaners in the same habitat. The pill bugs eat faeces, mould, and leftovers. They are sometimes caught and fed to pets such as lizards, but this is not recommended since those animals might become poisoned.
The family Armadillidiidae is differentiated from other woodlouse families by the two-segmented nature of the antennal flagellum, by the form of the uropods, and by the ability to roll into a ball, or conglobate.
Within the family Armadillididae, fifteen genera are currently recognised:
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