THE HEMIPTERA 35 



teen-year cicada or locust which has the longest period 

 of metamorphosis of any known insect. After seventeen 

 years of life spent in burrowing in the soil, feeding upon 

 roots and other vegetable material, these cicadas make 

 their appearance, often in great numbers, in the spring 

 or early summer. The history of various broods in differ- 

 ent parts of the country is known, so that it can be pre- 

 dicted, years in advance, when they will appear in any 

 particular part of the country. The cicadas of the 

 southern states may complete their metamorphosis in 

 thirteen years. 



Many of the smaller Homoptera such as the little green 

 leaf hoppers are quite destructive to various species of 



FIG. 28. The bean aphis, Aphis rumicis Linn. Winged and wingless 

 females with enlarged antennae of the same. Greatly enlarged. (After 

 Essig.) 



plants. Some of the most injurious, as well as in some 

 respects the most interesting members of the group are 

 the aphids or plant lice. Many species do considerable 

 injury by sucking the juices of plants, as they multiply 

 with such remarkable rapidity that a plant may soon be 

 literally covered by the descendants of a single individual. 

 Aphids have the peculiarity of producing young from eggs 

 which are not fertilized, a process known as parthenogene- 

 sis, a word meaning virgin reproduction. Usually several 

 generations are produced in this way. These consist 

 generally of wingless females, but at times winged females 

 occur which may fly to another plant and give rise to a 

 new colony. After a number of parthenogenetic genera- 



