40 PRACTICAL ZOOLOGY 



cause of their small size and protective covering, these scale 

 insects often are not noticed until they become so numerous as 

 to be very destructive. Their powers of reproduction are re- 

 markable; it has been estimated that the progeny of a single 



FIG. 22. San Jose scales on bark of tree. Small circle above, natural size ; 

 small circle below, highly magnified. (Photo by O'Kane.) 



female would number over three billion in a single season if all 

 were to survive. Scale insects possess very long, slender pierc- 

 ing mouth parts, which are inserted into the plant to suck out 

 the sap. Not only does the tree become weakened because 

 of the loss of sap, but it is also poisoned by a secretion injected 



