Country diary: gripped by a grayling's disappearing act

Dartmoor, Devon: I pinpoint the butterfly’s position and approach carefully, but somehow can’t locate itThe path ahead runs like a threadbare strip of carpet between low-lying vegetation. Scuffed by walkers, eroded by the elements and frayed by sheep, its worn matting of coarse grass scarcely covers the stony ground.As I follow it up the slope of this west Dartmoor hill I can hear on all sides the pistol-crack of gorse pods popping in the heat, firing their seeds around them, and sun