232 A COUNTRY READER. 



multiply. The parts of the plant thus attacked 

 shrivel for want of nourishment. 



When all the food in any particular part of a 

 plant is exhausted, some of the insects fly away 

 and start a fresh colony on another plant, and so 

 the work of destruction goes on. 



Fortunately for vegetation, these green flies 

 have many enemies. Starlings, sparrows, war- 

 blers, lady birds, and the larvae of many flies, 

 are particularly fond of them. Great numbers 

 are often killed by the wind and rain. 



It is only in very dry summers that they 

 increase enormously, and then it is that they do 

 so much mischief. 



Not only do green flies do harm by drawing 

 away the natural juices of the plant, but they 

 form a sugary, sticky substance. This substance 

 evaporating, leaves behind a shining, sticky, 

 solid substance, which closes up the little mouths 

 of the leaves through which the plant obtains its 

 nourishment. This sticky substance sometimes 

 drops on plants growing at the foot of the plant 

 attacked, or is carried by the wind to other 

 plants, and so great damage is caused. 



The spores or seeds of certain fungi produce 

 many plant diseases. These spores being blown 

 by the wind often adhere to the sticky substance 

 made by the green fly, and will then begin to 

 grow and multiply. 



