What classification do pillbugs fall under?

Pillbugs fall under the classification of Crustacea because they are part of the larger class that also includes crabs, lobsters, and shrimp. Crustaceans are primarily aquatic arthropods that typically have a hard exoskeleton and jointed limbs. Pillbugs, or roly-polies, are unique within this class as they are terrestrial and exhibit a body shape that allows them to roll into a ball as a form of defense. This characteristic, coupled with their gill-like structures that allow them to breathe moisture, further aligns them with other members of the crustacean group, which are usually found in aquatic environments.

In contrast, the other classifications provided do not apply to pillbugs. Insecta refers to insects, which have a distinct three-part body structure and typically undergo metamorphosis. Arachnida includes spiders and scorpions, which possess eight legs and lack antennae. Diptera encompasses flies and mosquitoes, characterized by having only one pair of wings and undergoing a different life cycle. Hence, classifying pillbugs as Crustacea appropriately reflects their biological and ecological characteristics.