I was drinking in the fresh air on the high earth wall of my farm dam last week, when I saw a low white cloud coming straight at me from the northwest. The distances you can see up here are immense, across tawny savannah towards blue hills on the horizon, an unfenced land stretching for days and days of travel to the Ethiopian frontier. As I was standing there, filling my lungs and feeling free and happy, the white mist got ever closer and began to resemble confetti. The low, fluttering cloud was entirely silent. And then I saw it was a multitude of white butterflies, all flying on exactly the same southeasterly bearing. In the days since, they have migrated in never-ending millions from dawn to dusk, pausing on flowers to fill up on nectar, before taking to the skies again.