248 



ZOOLOGY 



They suck the juices from stem and leaf. Plant 

 lice have a remarkable life history. Early in 

 the year eggs develop, into wingless females, 

 which produce living young, all females. These 

 in turn reproduce in a similar manner, until 

 the plant on which the}' live becomes over- 

 crowded and the food supply runs short. Then 

 a generation of winged aphids is produced. 

 These fly away to other plants, and reproduc- 

 tion goes on as before until the approach of 

 cold weather, when males and females appear. 

 Fertilized eggs are then produced which give 

 rise to young the following season. 



The aphids exude from the surface of the 

 body a sweet fluid called honeydew. This is 

 given off in such abundance that it is estimated 

 Maple scale, tive adults if au aphid Were the size of a cow it would 

 iVom°'photorr^h S'^^^ ^^^ thousaud quarts a day. This honey- 

 eniarged twice, by dew is greatly esteemed by other insects, es- 

 pecially the ants. For the purpose of obtaining 

 it, some ants care for the aphids, even providing food and shelter 

 for them. In return the aphid, stimulated by a stroking move- 

 ment of the antenna of the ant, gives up the honeydew to its 

 protector. 



Some aphids are extremely destructive to vegetation. One, the 

 grape Phylloxera, yearly destroys immense numbers of vines in 

 the vineyards of France, Germany, and California. 



The Order Hymenoptera 



This order contains some of the most highly developed insects. 

 We have already learned something of the structure and habits 

 of the bees, in connection with the study of the pollination of 

 flowers. Let us now find out about their wonderful communal 

 life. In the order Hymenoptera are placed bees, ants, and wasps, 

 insects which have developed a complicated social life. In connec- 

 tion with this communal life, nature has worked out a division of 



