or fear my behaviour might seem odd, I wait, sitting casually on the side of the bridge until the last group of walkers has moved on. Only then do I jump down the three-foot drop, landing with a splash into the ankle-deep stream. Crouching low, I move under the bridge, my torch lighting the gloom. I enter a secret world, hidden and immersed in darkness, with just the trickle of the stream. The noise of my wading footsteps is magnified. With the torch, I scan the underside of the wooden sleepers that make this bridge, and at first I think I’m unlucky. Then I spot, hanging like a dry brown leaf, the first peacock butterfly, with its flocked texture and muted browns. Now that my eyes know what to find, I discover 10 of them, some clustered in little groups. Butterflies that overwinter as adults, such as peacocks, commas and small tortoiseshells, choose somewhere secluded to seek protection from frost until they emerge into the early spring sunshine. During their torpor, some of the sugar in their blood is turned into glycerol, which works as antifreeze. Unlike other butterflies, which may be more likely to be predated by birds during hibernation, peacocks, if disturbed, have some shock defensive tactics. My disturbance caused one to suddenly open its wings. It flashed those false eye-spots at me and emitted a peculiar rasping hiss, created by rubbing its front and rear wings over each other. In the low light, it looked convincingly owlish. Enough to make me jump, and enough to cause any small bird to leave it alone. It puzzled me that these solitary insects found this place together. They like surprisingly cool, damp, undisturbed places, and it may be that the pheromones they emit to find a mate in spring can help them to gather, ready for breeding next year. After all, they will only live for a few weeks after mating and egg laying. I’m about to clamber out when I hear voices. Two walkers clip-clop over my bridge, chatting. I feel like a troll. I can’t appear in front of them – they would be horrified. Instead, I hunker down with the butterflies, waiting and feeling insane. But I’m smiling. Troll life is fun.