Insects are the most successful group of living organisms constituting almost 60% of described species. Animals first appeared on land between 500 and 400 million years ago. Insects were the first group of animals to evolve powered flight around 400 million years ago. Powered flight gives insects an advantage in exploiting patchy resources. Think of the difference flying makes to a bee that can flit from flower to flower compared to a bee that must walk up and down stems to reach the flowers. The flying bee can move faster and more efficiently. It can exploit resources in a way that a walking insect could not.
Another adaptation that made some insects successful is complete metamorphosis, the development of morphologically very different larval and adult stages connected by a pupal stage. The evolution of complete metamorphosis dates to about 344 million years ago, about 60 million years after the first flight. Today, 90 percent of described insect species have complete metamorphosis. Why is complete metamorphosis so advantageous? Complete metamorphosis with the transitional pupa stage liberates insects from constraints on adaptation. Changes in larval morphology are not limited by the need accommodate the change to adult. A larva, freed from constraints of transformation, can adapt to growth and development. The evolution of complete metamorphosis has resulted in morphological forms of larvae that have much more diverse than the adult forms.