98 ORDER HEMIPTERA 



probably once a year at least. They feed for the most part 

 on the roots of trees and shrubs and woody plants occurring 

 in their location. When trees are cut away after the eggs 

 are dejjosited, some of the nymphs doubtless fail to develop, 

 but there are some that become mature. 



The uniformity in their appearance ma>- be accounted 

 for by the fact that those that did not come out at a definite 

 time had little chance of l)reeding and reproducing. They 

 occur throughout the eastern United States and the seven- 

 teen-year form mostly to the north of the latitude of the 

 Ohio river. To the south of that latitude there is a thirteen- 

 year form. They do not occur over the whole area of the 

 country in which they may be considered as native, there 

 being portions where they do not occur at all, other places 

 where they occur twice in seventeen years, and still other 

 places where they occur three times in seventeen years. 

 They may be descendants of a generalized mass of cicadas 

 with a shorter life period. Just why they have been retarded 

 is another problem. Their subterranean habit and conse- 

 quent slow growth might serve to prolong their life. 



The dog-day cicada Avhich appears commonly in August, 

 lays its eggs in twigs of various trees, but the growth of 

 the nymph is much more rapid. The injury is the same as 

 in the seventeen-year cicada. The attacks of the adults 

 in young orchards are sometimes serious. 



After the Cicadidse the Membracidse are perhaps the 

 most generalized, though they present a specialized struct- 

 ure of the thorax. They are called treehoppers, the majority 

 inhabiting trees and shrubs, a few only occurring on her- 

 baceous plants. The specialization of the thorax is shown 

 in various ways. The prothorax is the greatest part of the 

 body visible from above. There are many variations and 

 these result in a great many forms of mimicry and protec- 

 tive resemblance. Some forms have the ])osterior part of 

 the prothorax broken up into globular pieces simulating the 

 body of an ant. In some cases there are three large knobs 

 which hang out from the central part and probably resemble 

 parts of the tree on which it occurs. They take on the 



