The individuals that belong to a same species of living organism are usually quite similar in appearance: they have the same structure and coloring. For example, tortoiseshell butterflies are easily distinguishable from brimstone butterflies. Individuals belonging to the same species can recognize one another and reproduce with one another. 

A group of animals can contain many species. For example, there are thousands of different butterfly species in the world. These groups can then be combined to form even larger groups, based on structural and genetic similarities. By doing so, we can classify both butterflies and beetles as insects, and both insects and spiders as invertebrates. 

In this manner, each species can be classified as belonging to larger and smaller groups. For example, a tortoiseshell butterfly is:

• an animal
• an invertebrate
• an arthropod
• an insect
• a butterfly
• a tortoiseshell butterfly