The individuals of a species often look alike: they have a similar colouring and structure. For example, the small tortoiseshell species of butterfly (Aglais urticae) is easy to distinguish from the common brimstone species of butterly (Gonepteryx rhamni). The individuals of a species recognize each other and are able to reproduce with one another.

A group of animals consists of multiple related species. For example, hundreds of butterfly species are found in Finland. Smaller groups of animals link together to form larger groups of animals. For example, butterflies belong to the group of insects along with beetles, dragonflies, and other similar organisms. 

Each species belongs to these kinds of groups. For example, the small tortoiseshell is: