Insects are small animals that have six jointed legs and three body parts (the head, the thorax, and the abdomen). Many insects can fly; flying insects have one or two pairs of wings. Some flying insects include butterflies, moths, dragonflies, flies, and mosquitos. Some non-flying insects include springtails, fleas, and lice.

Fish are swimming animals that have scales and fins. Fish breathe oxygen that is dissolved in the water using gills. Most fish have bony skeletons, but some, like sharks and rays, have only cartilage.

Amphibians are animals that begin their life in the water, breathing with gills. As they grow, they breathe air using lungs, and many move to the land. Some amphibians include frogs, toads, salamanders, and newts.

Reptiles are cold-blooded animals with scales. Some reptiles are: the dinosaurs, lizards, crocodilians, and snakes.

Birds are animals that have feathers, wings, a beak, hollow bones, and an efficient, one-way breathing system. Most birds can fly, but some cannot. The biggest bird (and the fastest-running bird) is the ostrich, a flightless bird. The smallest bird is a type of hummingbird that is only as big as a moth.