The best indication of the hobby’s hunting prowess is that this falcon elicits specific vocal responses from some of its prey, including swallows and martins. In swallow-speak, “hobby” and “deep danger” are synonyms. That’s because hobbies have the agility to take some of the world’s most notable winged organisms – swifts, dragonflies, swallows – in flight. The oak eggar moth is another of these aerial marvels, although you might not think it if you met the caterpillar. The larvae are the thickness of your little finger, with intermittent hoops of black and tawny smothered with long, potentially irritating hairs. They seem to understand their toxic properties and will walk across your open palm unperturbed. Yet the fat-bodied moth is of a different mindset, and with broad wings it flies in jinking zigzags, filled paradoxically with purpose and unpredictability. An exquisite test of optical prowess is to follow one with your binoculars. Flying oak eggars require an ocular rodeo that usually lasts just seconds before you’re bucked off and the moth is lost to view. So catching one in midair is remarkable. Two hobbies swung over the moor in long, looping, easy passages, and it was never more than a minute before they locked on to the next moth. Some were snapped up in a single pass, their winnowed wings fluttering down as the falcon flew. Yet one such chase was a story with seven chapters. You saw the survival benefits of a flight style that entails endless directional changes, because the hobby’s usual sweetness of flow was filled with sudden chops and shifts in angle. Each time the bird closed, the insect looped down or rose, and the hobby went blundering on until it came back around like a bull after the toreador’s cape. This time, the last time, the seventh attack, I could intuit that the chase would not go on when the moth sailed away from Earth and out into dangerous space. The hobby rose in an even and controlled and business-like fury, coming from below, undercarriage down and pressed foremost, wings flung wide and in the moment of connection you had the sense that the whole world knew how this must end. Country diary is on Twitter at @gdncountrydiary Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 (Guardian Faber) is published on 26 September; pre-order now at the guardianbookshop.com and get a 20% discount