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ARTHROPODA 



The several species of Aphidse bearing a white cottony 

 growth are known as wooly plant lice. In all there are 

 over a thousand species of Aphidae. Many of them give 

 forth from the alimentary canal a honey dew much sought 

 after by the ants, which often care for the eggs and young 



FIG. 106. Hop louse which lives on the plum tree in late fall, winter, and early 

 spring until the hop vines develop ; a, male ; b, female. Enlarged twenty 

 times. After Biley. 



of the lice by carrying them from place to place and other- 

 wise protecting them. Plant lice are therefore spoken of 

 as the ants' cows. 



Scale Insects or Bark Lice (Coccidae) 



The individuals of this family are easily recognized by 

 the fact that the female and sometimes the male dwell 

 beneath a scale varying in size from one fiftieth of an inch 

 to a fourth of an inch in diameter. The scale is formed 

 by the molted skins and excretions of the insect. 



Pernicious or San Jose Scale (Aspidiotus perniciosus.) 



