CHAPTER XII 

 ORDER CORRODENTIA* 



The Psocids and the Book-lice 



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Fig. 13: 



Psoius venosus. 



The winged members of this order have four membranous wings, with the 

 veins prominent, but with comparatively few cross-veins; the fore wings are 

 larger than the hind wings; and both pairs when not in use are placed roof- 

 like over the body, being almost vertical, and not folded in plaits. The 

 mouth-parts are formed for chewing. The metamorphosis is incomplete. 



The best-known representatives of this order are the minute, soft- 

 bodied insects which are common in old papers, books, and neglected col- 

 lections and which have received the popular 

 name of book-lice. These low, wingless creatures 

 form, however, but a small part of the order. 

 The more typical winged forms (Fig. 132) bear 

 a strong resemblance to plant-lice or aphids. 

 The body is oval, the head free, and the protho- 

 rax small. The fore wings are larger than the 

 hind wings ; and both pairs when not in use are 

 placed roof-like over the body, being almost 

 vertical, and not folded in plaits. The mouth- 

 parts are plainly chewing. The mandibles are of the ordinary, strong, 

 heavy, biting type. The maxillas consist each of a body piece, a weak ter- 

 minal lobe, and a four-segmented palpus. 



The venation of the wings is characteristic in this order, see page 84. 

 The venation is more or less reduced; but its most characteristic feature 

 is the bracing of the wing by anastomoses of the principal veins instead 

 of by cross-veins, although there are one or two cross-veins in some species. 



The Corrodentia of the United States and Canada represent two fam- 

 ilies, which can be separated as follows. 



A. Wings well developed; ocelli present Psocids 



AA. Wings absent or vestigial; ocelli absent Atropine 



Family Psocids 



The Psocids 



The family Psocidae includes the more typical members of the Corro- 

 dentia, those in which the wings are well developed (Fig. 132). Usually 

 the wings extend much beyond the end of the abdomen; but short- 

 winged forms occur in species which ordinarily are long-winged. Of 

 course the young of all are wingless, and there is a gradual development 

 as the insect matures. 



* Corrodentia: Latin corrodens, gnawing. 

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