Found in our bath a few mornings back: a silverfish Lepisma saccharina (Thysanura: Lepismatidae ). This is the most familiar species of the Thysanura, the bristletails, which are an order of insects that have never, in the whole of their evolutionary history, had wings.
According to Michael Chinery (Complete British Insects, Collins, 2005, page 11), silverfish eat "a variety of starchy materials including the glue of cartons and bookbindings". We often discover them on the bathroom floor in when we switch the light on in the night. There they presumably feed on maize starch in the talcum powder that my wife and daughter spill.
Photos taken in Reading, UK, on 2010-04-10.