Most of the animals that live around us on land and in the oceans are invertebrates - animals that do not have backbones and jointed internal skeletons like ours. Many have tough external skeletons, while others have hard shells. But many more have soft, muscular bodies with no hard skeletal parts at all.
The animal kingdom is divided into 35 major groups, each called a phylum, and each phylum is divided into classes. The vertebrates make up part of just one phylum.
The biggest invertebrate group consists of the arthropods. They include the insects, spiders and scorpions, and crustaceans. Adult arthropods have tough, jointed external skeletons or exoskeletons, several pairs of jointed legs, and - in the case of insects - wings.
Both in terms of species and sheer numbers, insects outnumber all other animals on Earth. They are the most plentiful creatures on the planet.
More than a million different species of insects have been scientifically named and described, and thousands more are discovered every year. Thanks to their amazing adaptations, they flourish in every land habitat and play a key role in the global ecosystem, recycling dead plants and animals, pollinating flowering plants, and providing food for a host of bigger animals. In fact, insects are so vital to life on Earth that we could not survive without them.