OUTLINES OF ENTOMOLOGY. 107 



and drop to the ground, into which they burrow and where they remain, 

 descending- deeper and deeper year by year, feeding on the rootlets of 

 trees and growing very slowly, until ready to change to pupje, when 

 they begin to ascend. The pupa is active, and after emerging from the 

 ground crawls to the trunk of some tree or shrub, to which it clings 

 with its spiny claws, while the perfect cicada emerges. As these pupa 

 shells retain their form, except for the slit on the top, through which 

 the imago escaped, they are often mistaken for dead "locusts," and 

 it used to be a popular superstition that they " sang until they burst." 

 They appear in May or Juue. 



The annual Dog-day or Harvest-flies, of which there are but two 

 or three, not very distinct species, in this country, develop about mid- 

 summer, and sing- late in the afternoon and in the twilight, until frost. 

 The most common species is somewhat larger than the seventeen-year 

 species, of a green and black color, having the body thickly covered 

 by a whitish powder or "bloom," from which circumstance it received 

 its name, Cicada pruinosa, Say. 



The Tree-hoppers (Membracid^) are rather email insects, but 

 among them are some of the most singular and grotesque forms of 

 animate life. The pro-thorax is the part most subject to variation. 

 This often extends backward almost to the tip of the abdomen, or the 

 front edge is prolonged into a horn that curves far over the head. 



The Buffalo Tree-hopper fCeresa buhalus, Fabr.) exhibits in its 

 form a variety of triangles ; in front, on top, and on each side, one or 

 more of these geometric figures can be traced. It is of a dull green 

 color, nearly one-half inch in length, and the female often does consid- 

 erable damage to the tender twigs of fruit trees by the numerous slits 

 which she saws in them for the reception of her eggs. 



Among the Leaf-hoppers (Jassid^) are a number of small, but 

 very destructive species. These insects have oblong forms, long 

 wings, often beautifully colored, a rounded pro-thorax and a triangular 

 head. A few are about one-half inch in length, but the greater number 

 are very small. The Grape-vine Leaf-hopper {Erythroneura vitis, Har.), 

 commonly but erroneously called " Thrips," frets the leaves of the vine 

 with innumerable punctures until they turn brown and wither. These 

 insects are often so numerous late in summer that they leap off in 

 clouds when the vines are shaken. Other species are injurious to 

 roses, growing grain and grass. 



The Plant-lice (Aphidid^) are a very comprehensive and interest- 

 ing class of insects. They range from small to exceedingly minute, 

 but make up in numbers what they lack in size, and include some of 

 the most destructive pests known to the agriculturist. They are soft- 



