"The Very Hungry Caterpillar" is Carle's third book, and uses distinctive collage illustrations which were innovative at the time of publication, 'eaten' holes in the pages and simple text with educational themes – counting, the days of the week, foods, and a butterfly's life stages. It teaches children how to count and to make one-to-one correspondences between numbers and the items the Very Hungry Caterpillar has eaten. There have been many related books and other products, including educational tools, created in connection to the book. The Very Hungry Caterpillar's diet is fictional rather than scientifically accurate, but the book introduces concepts of Lepidoptera life stages where transformations take place including the ultimate metamorphosis from 'hungry caterpillar' to 'beautiful butterfly', and it has been endorsed by the Royal Entomological Society.