14 



ZOOLOGY 



The Homoptera include insects of very diverse size and 

 form. The largest are the cicadas, or "locusts" (Fig. 14), 

 some of which have the remarkable habit of requiring 

 thirteen or seventeen years for their development. Con- 

 sequently these cicadas 

 appear only at intervals 

 of thirteen or seventeen 

 years. The young bury 

 themselves in the 

 ground and live by 

 sucking juices from the 

 roots of trees. Eventu- 

 ally they come to the 

 surface, leave their lar- 

 val skin (Fig. 15), and 

 fly away as full grown 

 cicadas. In the case of 

 our common species of cicada there is a brood every year. 

 Besides the cicadas the Homoptera include the little 

 leaf-hoppers and tree-hoppers, the very destructive scale- 

 bugs (Fig. 16), and the mealy-bugs, most of which attack 

 fruit trees and their fruits, and the plant-lice, or aphids 

 (Fig. 17). 



FIG. 17. Schizoneura, a woolly aphis, on 

 apple twig. Photo, by V. H. L. 



APPENDIX TO CHAPTER I 



KEY TO THE PRINCIPAL FAMILIES OF THE ORTHOPTERA 



a\. Legs similar, fitted for running . , ; . , Blattidce 



(Cockroaches) 



2 - First pair of legs differentiated for grasping ; pro- 

 thorax elongated . ; . . . . Mantidce 



(Praying-man ti s) 



