CHAPTER VIII 



THE BOOK-LICE AND BARK-LICE (Order Corrodentia) 

 AND THE BITING BIRD-LICE (Order Mallophaga) 



OMETIMES in taking from the shelves an old 

 book, long untouched, there may be seen, on 

 turning its leaves, numerous extremely minute, 

 pale-colored, wingless insects, the book-lice, or 

 dust-lice. So small are they, indeed, that a 

 reading-glass or hand-lens will be needed to make 

 out anything of their real appearance. They 



run about rather swiftly and seek to conceal their soft, defenceless little 

 bodies somewhere in the binding. Under the lens they are seen to have 

 a rather broad, flattened body (Fig. 140), six short legs, no wings (although 

 sometimes tiny wing-pads are present), long, slender antennae, and a pair of 

 small black spots on the head, the simple eyes. There is a distinct neck, 

 the head being free, and plainly wider than the prothorax. The abdomen 

 is nearly oval in outline. There are no distinctive markings or pronounced 

 chitinization of the soft body-wall. These book-lice can be found else- 

 where than in old books; they feed on dry, dead organic matter, the 

 paste of the book-bindings and the paper, and are common in birds' nests, 

 where they feed on the cast-off feathers, in the crevices of bark, and on 

 old splintered fences, where they feed on moulds and dead lichens. 



Certain other insects closely related to the book-lice are not so small and 

 simple, however, some having two pairs of wings and a plump, rounded 

 body (Fig. 141); these look much like plant-lice (Aphids). These winged 

 kinds do not live in libraries, moreover, and the name "book-lice" is a 

 misnomer for them. They are rarely seen by persons not trained entomolo- 

 gists, and indeed are not at all familiar to professed students of insects. 



The life-history of these obscure insects has been but little studied, but it 

 is of a simple kind, the metamorphosis being incomplete, and in the case 

 of the wingless forms certainly very slight. The young of the wingless forms 

 " greatly resemble the old, but have no ocelli or wings, and sometimes the 

 tarsi are of two joints, while in the adult they have three." The structure 

 of the adults presents no points of particular interest except in the case of 

 the mouth. The book-lice have biting mouth-parts, the jaws being strong 

 and heavy for the successful mastication of the hard dry food. In the throat 



