What insect order contains beetles?

The insect order containing beetles is Coleoptera.

The name comes from Greek roots meaning “sheath wing,” referring to the hardened forewings called elytra. These protective wing-cases meet along the beetle’s back and cover the delicate flying wings beneath. Beetles use their elytra mainly as armor, while the membranous hindwings provide powered flight in many species.

Coleoptera is the largest insect order, with roughly 400,000 described species. Its members include weevils, scarabs, lady beetles, fireflies, click beetles and longhorn beetles. Most undergo complete metamorphosis: egg, larva, pupa and adult. A common mix-up is confusing beetles with bugs; in strict entomological usage, “true bugs” belong to Hemiptera and typically have piercing-sucking mouthparts, whereas beetles have hardened forewings and usually chewing mandibles.