Totalling an estimated 10 million species, the insects and their close relatives are the most abundant and diverse group of animals in the world, so what is the secret of their success? Their hard external skeleton provides strength and protection and their small size allows them to exploit many microhabitats. In Yellowstone, Steve Backshall reveals how teamwork allows a colony of bees to scare off a hungry bear, and in Australia this same teamwork allows a colony of ants to beat the rising tide. But to unlock the real secret of their success Steve visits the Swiss Alps, where an incredible relationship exists between the ant, the wasp and the butterfly.