About 75% of all animal species are arthropods. There are more different types of arthropod than any other group on the plant. Arthropods include insects, spiders, crabs, lobsters, barnacles, centipedes, and even hundreds of extinct species in fossils.
This post from Biology4Kids explains the four major types of arthropod, their exoskeleton, metamorphosis, and the 26 orders in the Class Insecta. That’s a lotta bugs!