A tiny ant makes marathon journeys over the scorching desert. An albatross flies 800 miles over open ocean before returning with food for its chick. Hundreds of lobsters march in columns over the seabed to avoid storms. All find their way with an accuracy that we have only recently achieved.

David Attenborough looks at how, for better or worse, many animals form surprising partnerships. Birds rid larger animals of itchy hangers-on, hermit crabs enlist stinging anemones to repel predatory octopuses and others use their hosts in less benign ways.