On the eve of the Euro 2016 final between France and Portugal, ground staff at the gigantic Stade de France in Paris had left the stadium’s lights on, for security reasons. Attracted by the blinding floodlights, thousands upon thousands of migrating Silver Y moths descended into the empty arena. Those not killed by the heat of the lamps eventually ended up among the grass of the playing surface, where, after the lights were turned off, they hid throughout the day of the big match. As evening fell, 80,000 spectators took their seats and the lights were turned back on. The sleeping moths stirred, and soon thousands were zigzagging among the players. Photographs taken that night show annoyed football officials picking moths off each other’s suits, while the swarm blocked the lenses of TV cameras and hung from the goalposts. Perhaps the highlight came when Cristiano Ronaldo sat injured and weeping on the pitch, while a lone Silver Y sipped his teardrops away.As the Portuguese superstar had discovered, the mingling of urban development with the natural world can throw up some weird and wonderful occurrences. Cities are like mad scientists, creating their own crazy ecological concoctions by throwing all kinds of native and foreign elements into the urban melting pot, then spicing it up with artificial light, pollution, impervious surfaces and a host of other challenges. Researchers around the globe are documenting how globalisation and urbanisation are changing the behaviour and evolution of animals.Indeed, evolutionary biologists no longer need to travel to remote places like the Galápagos todiscover their holy grail: speciation, the formation of new and distinct species in the course of evolution. The process is going on right in the very cities where they live and work. In tune with their human population, cities have been assembled from immigrants from around the globe.