160 



APPLIED EJ^TOMOLOGY 



are held at a sharp angle over the body, hinder margins uppermost. An- 

 tennce long and slender. Tarsi of two or three segments. Ocelli sometimes 

 present in the adult condition. Metamorphosis incomplete. 



This little order contains few species of much economic importance. 

 The wingless forms — book-lice (Fig. 152) — found in buildings, eat the 

 paste and paper of old books and are also found in birds' nests where 

 they find in feathers and other organic debris their food. The winged 

 forms, frequently called Psocids, are found in various places, but perhaps 

 most frequently on the trunks of trees, generally in clusters and often in 

 various stages of their development. They have the power of producing 

 silk and sometimes the clusters appear to be covered, at least partly, by 

 a web of this. 



Fig. 153. — Adult Psocids: a, side view showing position of wings at rest; 6, Psocid 

 (Psocus lineatus) with wings spread. Both greatly enlarged. {From Sanderson and 

 Jackson, Elementary Entmology: a, after Kellogg: b, after J. B. Smith.) 



Some of the book-lice are claimed to be able to make a ticking sound 

 something like that of a watch, and this sound is often called the "death 

 watch," Such a sound is certainly produced by a small beetle, and the 

 possibility of the book-lice also being able to make it has been questioned. 

 The weight of evidence thus far, however, seems to favor this possibility. 

 It is heard chiefly in old houses at night or when everything is quiet, as 

 a faint, rapidly repeated tick-tick-tick, and is in all probability, the call 

 of an insect to its mate. 



The winged Corrodentia (Psocids, Fig. 153) are not known to be of 

 any economic importance. Where the wingless forms (book-lice) be- 

 come extremely abundant in buildings, relief may be obtained by a 

 thorough cleaning of the infested places. Light and air, particularly 

 dry air, are unfavorable to them, and heating a room to quite a high 

 temperature for a few hours and the exposure of all the furniture to 

 sunlight for a time on a bright day will generally free the place from these 

 insects. All stages except the egg appear to die at the beginning of 

 winter. 



