20 PRACTICAL ZOOLOGY 



undergo indirect metamorphosis. They hatch from the eggs 

 as wormlike larvae, grow in size for a time, and then enter a 

 stage of rest, when they are spoken of as pupa?. During the 

 pupal stage the adult insect develops within the pupal covering 

 and finally breaks out fully formed. The larva; of butterflies 

 and moths are called caterpillars; those of beetles, grubs; and 

 those of flies, maggots. The pupae of butterflies and moths are 

 popularly known as chrysalids. The chrysalis is often covered 

 by a cocoon spun by the larva. 



Relations to Man. — Grasshoppers are valuable for the pur- 

 pose of studying structure and function. They are important 

 also because of the injuries they inflict upon crops in order to 

 satisfy their hunger. There are plenty of noxious weeds that 

 the grasshoppers might devour with benefit both to themselves 

 and to the farmer, but they persist in destroying many kinds 

 of useful plants instead. 



The most notorious grasshoppers in this country are the 

 Rocky Mountain or migratory locusts. These insects were 

 particularly destructive in the states of the western part of the 

 Mississippi Valley in the years 1873 to 1876. Their native 

 breeding grounds are in the highlands of Montana, Wyoming, 

 and Colorado, but when the locusts become excessively abun- 

 dant, they spread eastward, flying with the wind, as much as 

 two hundred or three hundred miles in a single day. Their 

 ravages in the seventies were described by a commission of men 

 appointed by Congress to report upon them as follows: — 



" Falling upon a cornfield, the insects convert in a few hours 

 the green and promising acres into a desolate stretch of bare, 

 spindling stalks and stubs. . . . Their flight may be likened 

 to an immense snow-storm, extending from the ground to a 

 height at which our visual organs perceive them only as minute, 

 darting scintillations, leaving the imagination to picture them 

 indefinite distances beyond. ... In alighting, they circle in 

 myriads about you, beating against everything animate or in- 

 animate, driving into open doors and windows, heaping about 



