Beetles are insects that make up the order Coleoptera, which, at over 400,000 species, is the largest order of insects by far. Around 40% of all insects fall into this order. You can find beetles everywhere, from the swamp to the desert to the mountains, and they feed on everything from plant matter to meat to dung.
The thing all types of beetles have in common is their elytra, which is the pair of heavily armored forewings that protect the beetle's abdomen. Sometimes, these encase a single pair of wings that allow the beetle to fly. Other times, these armored cases may only protect the beetle's body because there are no wings underneath.