122 



ELEMENTARY ENTOMOLOGY 



of these vermin is shown in Fig. 165. Similar species infest horses, 

 cattle, and other domestic animals, as well as many wild mammals. 



SUBORDER HOMOPTERA 



The cicadas (Cicadidae). The common dog-day harvest-fly 

 (Fig. 1 66) is the best known example of this interesting family; 

 and although we seldom see it, we are made aware of its presence 

 on a hot summer day by the shrill calls answered back and forth 

 from the tree tops. It is black and green in coloi\ more or less 

 powdered with white beneath. The most remarkable member of 



FIG. 166. Dog-day harvest-fly (Cicada tibicen], female 

 (After Lugger) 



the family is the periodical cicada, often improperly called the 

 seventeen-year locust, from its habit of appearing in immense 

 numbers every seventeen years. It is of course entirely unrelated 

 to the true locusts, or grasshoppers. The adults lay their eggs in 

 the twigs of trees, often seriously injuring young fruit trees, as the 

 twigs or stems die beyond the point of the egg puncture. The 

 nymphs drop to the ground upon hatching and, burrowing into 

 the earth, feed upon the roots of trees for sixteen years. The 

 seventeenth year they emerge in immense numbers within a few 

 days, crawl up the trunks of trees, fences, buildings, etc., and trans- 

 form to the adults, which are blackish, with orange markings on 

 the wings. For the next few weeks the air is filled with their 

 shrill cries, and soon many affected trees turn brown as a result of 



