The mighty Indian banyan tree (Ficus benghalensis L) is pollinated by a tiny wasp, Eupristina masoni, which lives inside the ovaries of its miniscule flowers. The banyan tree, like every other species of fig (genus Ficus), hides its flowers inside the chamber of an urn-shaped inflorescence, which can be accessed only by fig insects (family Agaonidae). Similarly, each of the approximately 900 known Ficus species all over the world depends on a fig insect that is specific to that particular Ficus species, to reproduce. The fig insects lay eggs inside a few fig ovaries, and the larvae develop there. The Ficus, thus, provides food and accommodation to the developing fig insects by sacrificing several of their own offspring. Apart from providing food and space for these pollinators, and for other wasps that parasitise these pollinators, Ficus also provides food and shelter for a wide range of other animals—from thrips and ants, to apes and elephants—and therefore qualifies to be called a ‘keystone’ genus of tropical forests. Local extinction of fig insects due to habitat disturbance, changes in weather patterns, or for other reasons, can cause a breakdown of such a mutually beneficial relationship, which might lead to the extinction of Ficus species, thus triggering cascading effects on tropical forests. The ‘Ficus–fig insect mutualism’ best epitomises the importance of insects in the sustenance of the biosphere.