A symbol of global inequalities and shifting geopolitical fortunes, some passports offer their holders far more freedom to travel than others

Passports can resemble abridged memoirs, their stamps telling romantic stories of wanderlust, freedom and belonging.

But they are also a symbol of global inequalities and shifting geopolitical fortunes. Passports from some places allow their holders to travel abroad simply by booking a flight and packing a bag. Others, however, entail booking an appointment at the nearest consulate, presenting documents to prove identity and financial means, then waiting weeks for a decision.

Trillions of insects embark, largely unnoticed, on epic journeys every year across mountain ranges, deserts and seas, and it is only now, as their numbers suffer huge declines, that scientists are tracking their movements

On a cloudless sunny day in October 1950, ornithologists Elizabeth and David Lack stood on a mountain pass in the Pyrenees and observed a once-in-a-lifetime spectacle – clouds of migrating insects.

Up to 500 butterflies were fluttering past them every hour through the 2,200m-high Puerto de Bujaruelo mountain pass on the French-Spanish border. By mid-afternoon dragonflies were skimming through, outnumbering the butterflies by 10 to one. The spaces between were filled with thousands of tiny flies.