Scientists sort animals into groups by looking at their features (what their bodies are like and how they live).

Animals with a backbone (vertebrates) include: Mammals — have hair or fur and feed their young on milk; most give birth to live young. Birds — have feathers, a beak and two wings, and lay eggs with hard shells. Fish — live in water, breathe with gills and have fins; most have scales. Reptiles — have dry, scaly skin; most lay eggs. Amphibians — have moist skin and usually begin life in water.

Animals without a backbone (invertebrates) include insects. Adult insects have six legs and three body parts (head, thorax and abdomen). Spiders and worms are invertebrates too, but they are not insects.

Some animals are tricky! A bat can fly, but it has fur and feeds its young on milk, so it is a mammal. A penguin cannot fly, but it has feathers, so it is a bird.