pillbug

noun

1. any of various small terrestrial isopods, especially of the genera Armadillidium and Oniscus, which can roll themselves up into a spherical shape.

noun

1. any of various woodlice of the genera Armadillidium and Oniscus, capable of rolling up into a ball when disturbed

n.also pill-bug, 1841, from pill (n.) + bug (n.).