Whilst the bigger beetle, _Xestobium_, is the common death-watch, it has been proved that the little furniture beetle, _Anobium_, is also a tapper, making regular and persistent strokes like the ticking of a watch. Another insect, called the book-louse (_Atropos divinatoria_), very minute, only one-twentieth of an inch, soft, white, and wingless, not a beetle at all, but also a devourer of literature (Fig. 64), is declared by some good observers to be a “ticker” or “tapper,” but other naturalists deny that it can make such sounds. It seems unlikely on account of the extremely small size and softness of the book-louse, but the matter needs further investigation. [Illustration: FIG. 63.—The silver-fish insect (_Lepisma saccharina_). The line to the right shows its natural size.] A curious fact is that the grubs of beetles such as _Anobium_ and _Xestobium_ (or other closely allied kinds) are not arrested in their tunnelling by soft metal. They cannot tackle iron plate or brass sheeting, but they will penetrate tinfoil and, what is more astonishing, lead plate and leaden waterpipes. Specimens showing such perforations are in the museums of Oxford and London, and I have received an account of a lead pipe packed in wood in the wall of a house being perforated by these beetle-grubs. Once at work on the wood, “the straightforward intentions” of the grub are not to be diverted by such an obstacle as lead: it goes straight on through the lead as it would through the cover of a book or a knot in the wood. [Illustration: FIG. 64.—The book-louse, or _Atropos divinatoria_, a soft, cream-coloured, wingless insect smaller than a flea. It is believed by some observers to be capable of making sounds like the ticking of a watch.]