Down at the realm of the very tiny, your house teems with life: it is a veritable rainforest for crawling, clambering things. Armies of tiny creatures patrol the boundless jungles of your carpet fibres, paraglide amid floating motes of dust, crawl across the bedsheets at night to graze upon the vast, delicious, gently heaving mountain of slumbering flesh that is you. These creatures exist in numbers you cannot comfortably imagine. Your bed alone, if it is averagely clean, averagely old, averagely dimensioned and turned averagely often (which is to say almost never), is likely to be home to some two million tiny bed mites … It has been calculated that if your pillow is six years old (which is the average age for a pillow), one tenth of its weight will be made up of sloughed skin, living and dead mites, and mite dung - or frass, as it is known to entomologists.
Bill Bryson, At Home: A Short History of Private Life