GARDEN INSECTS 213 



after growing for about two weeks they will begin to give 

 birth to living young — very small, but perfectly formed 

 aphids — at the rate of possibly two or three a day. These 

 also are females and, attaining their growth in a few days, 

 in turn produce living young at this astonishing rate. 

 Meanwhile, if we keep watch of the cherry trees, we may 

 observe the increase of the aphids from a single one here 

 and there to millions, covering the leaves, growing shoots, 

 and even fruit, with disgusting black masses of the insects. 

 When we think that the trees are about to be killed, a 

 winged generation appears which leaves the cherry trees 

 for some other plant. It is possible that this migration 

 has been developed to save both trees and insects. It 

 occurs generally about the time the cherries ripen, but to 

 what plant they go has not been determined. In the fall 

 winged females find their way back to the cherry trees, 

 the eggs are laid behind the buds, and the year's cycle is 

 completed. 



Most of our common species of aphids present a similar 

 life story. So far as is known, some do not migrate 

 from one plant to another. A few, like the woolly aphid 

 of the alder, have not been discovered to lay eggs, but pass 

 the winter in the adult form in protected crevices about 

 the bark and roots of their food trees, covered by their 

 woolly coats. 



Living the easy life of a parasite, sucking the nutritious 

 juices of plants, aphids multiply at a most astonishing rate. 

 Possibly for a month or so in the spring the class may 

 arrange to have a single aphid on some convenient food 

 plant and may be able to count from week to week the 

 numbers produced. This will furnish the data for an 



