At the moment, life feels like one long goodbye. Swallows are departing, house martins gathering and bumble bees slipping into hibernation. Last weekend, on perhaps the final warm Saturday of the year, I sat working with the windows open; one after another, some of my summer companions drifted in, as though bidding farewell. First of all, loud buzzing announced a wasp. Droning heavily around the room, it landed on my keyboard before heading back out the way it came. Next, a red admiral butterfly filled the room with colour and life. Chances are this was the offspring of migrants – most UK red admirals arrive from central Europe in spring and early summer, they then lay eggs, which mature into adults about now. As its deceptively powerful wings fanned my face, I guided it to the wind