Biodiversity means the variety of life in all its forms. It includes the variety of species and ecosystems in the world, and genetic variation. Invertebrates are one of the largest and most accessible groups of animals for primary children to study. In this article, the author explains why and how children should engage with the idea of biodiversity. She stresses the study of invertebrates, such as earthworms and ants, which offers an important window on biodiversity in a significant habitat--soil. Revealing the biological diversity of these animals and their myriad roles in the web of life engages children with a concept that is crucial to life on Earth.