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 
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