HOMOPTERA CICADIDAE 



569 



of the earth, but we have one species, a great rarity, in the ex- 

 treme south of England ; altogether there are about 800 species 

 known. These Insects are seen above ground so far as the 

 life-histories are at present known only in the perfect condi- 

 tion, the creatures in their earlier stages being subterranean and 

 living on roots. As soon as the individual comes out of the 

 ground it splits open the nymph-skin, and the perfect Cicada 

 emerges. One species the North American Cicada septendecim 

 is a most notorious Insect owing to its life-cycle of seventeen 



FIG. 280. Cicada septendecim. North America. (After Riley.) A, Larva; B, 

 nymph ; C, nymph skin after emergence of the imago, D ; E, section of twig with 

 series of eggs ; F, two eggs magnified. 



years. It is considered that the individual, after nearly seven- 

 teen years of underground existence, comes to the surface and 

 lives for a brief period the life of a noisy Insect. This is the 

 only Insect at present known having so considerable a longevity. 

 This fact, and several other peculiarities, have attracted much 

 attention, so that there is an extensive literature connected with 

 the seventeen-year Cicada. It has a wide distribution over the 

 United States, but does not confine its appearance to every 

 seventeenth year, being found somewhere or other frequently 

 in numerous localities almost every year. The evidence as to 

 its periodicity has been obtained by taking the locality and other 

 points into consideration as well as the year of appearance. 



