Imagine an innocent little beetle plodding across the forest floor, hunting for morsels to feed upon. Aha! It spies a cluster of bivalve leaves, each shiny red on the inside and offering an array of tantalizing nectar drops. Eager to explore, it picks its way onto one of the leaves.

Stories of unlikely animal friendships—an elephant playing with a dog, a gorilla nurturing a kitten, or birds of different species grooming one another—have long fascinated people.