How did the pill bug get its name?

Armadillidium vulgare. The name varies at times, but if you are referring to the grayish insect with many legs that rolls up into a ball when threatened, better known as the "roly poly," then its name is Armadillidium vulgare. It is also known as a sow bug. Armadillidium vulgare. The name varies at times, but if you are referring to the grayish insect with many legs that rolls up into a ball when threatened, better known as the "roly poly," then its name is Armadillidium vulgare. It is also known as a sow bug.