Scurrying across a damp page or a weathered piece of bark with a distinctive, jerky stop-start motion, the booklouse is the mould-grazer of the library and the forest floor alike. These tiny, soft-bodied insects, often no larger than a pinhead, are defined by a primitive anatomy featuring a large, bulbous head and specialised chewing mouthparts. Despite their common name, they are not true lice and do not feed on humans or animals. Instead, they are gleaners of the shelf that subsist on microscopic fungi, mould spores and the organic starches found in old book glues and wallpapers. This microscopic maintenance makes them a biological clean-up crew for the damp, indoor environments and shaded forest crevices of New Zealand. As sensitive indicators of humidity, booklice represent a state of domestic micro-wildness, appearing only when the atmospheric moisture is high enough to support the fungal growth they depend upon. In the New Zealand bush, their winged relatives known as barklice live in massive, communal silk-tents on the trunks of native trees, where they graze on algae and lichens. Their life cycle is an industrious process of subterranean and surface conversion, turning invisible mould into energy that feeds smaller predatory mites and spiders. This existence is a definitive sign of hidden environments, reminding us that even our most supposedly sterile spaces are teeming with life if the conditions of moisture and darkness are met. Not threatened, booklice are harmless residents that pose no structural threat to buildings, though their presence is a clear signal that the air is a little too damp for the preservation of paper. They are the silent witnesses to the aging of paper and the dampening of wood, proving that nothing organic is ever truly unoccupied. To encounter a booklouse darting across a shelf is to witness a survivor that has mastered the art of microscopic maintenance.