Butterflies crossing oceans, moths navigating by the stars: unravelling the mysteries of insect migrations

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. That day became the first record of fly migration in Europe – the skies were packed with tiny travellers on remarkable long-distance journeys unknown to science. It would be decades before the concept of insect migrations was widely followed up. Today, we know that insects – many of which have wings smaller than a human fingernail – are among the planet’s most prolific migrants, with trillions travelling large distances every year, including over deserts, mountain ranges a