OOK-LICE, OR PSOCIDS, are the tiny white or grayish-white insects, 
scarcely as long as the width of an ordinary pinhead, and often 
much smaller, that scurry across the pages when old, musty books are 
opened. 
They appear in houses in greatest numbers during late summer and 
early fall, and are more abundant in damp, well-shaded rooms not in 
general use, and in houses long closed. Very few are found in bright, 
sunny, dry rooms in constant use. 
Book-lice run in a halting fashion over everything in the house. They 
feed on all sorts of vegetable and animal matter. It is not often that 
they become abundant, and when they do, they attract attention more 
by their annoying presence than by the actual damage caused. They 
injure man in no way and are therefore unlike the true lice. 
Unless they are present in annoying numbers, it is probably not worth 
while to worry about book-lice, for many exist out of doors and can get 
in through cracks and through the mesh of ordinary screens. With the 
coming of cold weather, or in late fall and winter, book-lice die off, 
but may leave behind eggs that will hatch the following spring. Control 
measures, discussed on page 4, should be. resorted to when book-lice 
become unusually abundant. 
BOOK-LICE’ OR PSOCIDS. 
THEIR HABITS AND WHERE THEY THRIVE. 
WELLING HOUSES, libraries, museums, military barracks, 
storerooms, barns, and other buildings often harbor diminutive 
insects known as book-lice, or psocids. Although many of these 
doubtless enter from outside, those that become numerous enough to 
annoy occupants can live and multiply wholly within doors. 
Book-lice are found in all sorts of places, such as the trunks and 
foliage of trees, on fences, in woodpiles, and in refuse of all sorts: 
in fact, upon practically anything that has been left undisturbed 
for any length of time during warm and moist weather. 
The book-lice that occur in houses have no wings and are seldom 
one-sixteenth of an inch long, often much smaller. Their shape 
and appearance are shown by the figure on the title-page. They are 
pale colored, almost white when young, but as they grow older are 
darkened somewhat by the food they have eaten, for this shows 
through their more or less translucent bodies. When old, musty 
books are opened suddenly, the book-lice may be seen scurrying 
across the pages in a halting and uncertain fashion, and frequently 
they are noticed upon door screens, window panes, furniture, books, 
and photographs, or upon almost any object in the room. 
Book-lice do not attack man as do the true lice, and are, therefore, 
harmless to the occupants of a home. They are called book-lice 
1Insects of the order Corrodentia and family Psocidae. 
156483°—Bull. 1104—20 
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