THE LOWER ORDERS 



35 



bark scales of old apple trees where there is plenty of 

 moisture. Others may be found during the summer on de- 

 caying wood. 

 Still others are 

 classed as injur- 

 ious and attack 

 certain of our 

 garden crops. 

 Their injury is 

 rarely serious. 

 One form, called 

 the Snow-flea, is 

 found in the 

 early spring on 

 the surface of 

 patches of snow. 

 28. Corro- 

 dentia. Certain 

 small insects 

 called Book lice 

 and Psocids form 

 this order, which 

 is of slight im- 

 portance. The 

 book-lice are mi- 

 nute and may 

 be found on 

 books, mainly in 

 dark places and 



where the books are not frequently used. The Psocids 

 (Fig. 21, 4) are winged and live on plants. They resemble 

 large plant-lice more than any other common insects, but 

 have biting mouth-parts, while the plant lice suck sap. 



FIG. 21. Slightly reduced. 



1, Fish-moths (Thysanura) ; 2, Mayflies (Ephem- 

 erida) ; 3, Earwig (Euplexoptera) ; 4, Psocid (Corroden- 

 tia); 5, Stone-flies with nymph (Plecoptera) ; 6, Ter- 

 mites or white-ants (Isoptera), 



