90 AN ECONOMIC ENTOMOLOGY. 



in this stage their traveUing powers are limited, though their 

 appetite is not. Yet even now they are able to cover consider- 

 able distances if a short food supply makes it necessary. The 

 wing- pads, which become visible early in the nymphal life, increase 

 in size until the insect is ready for its final change, and when this 

 occurs its powers for destruction are multiplied by the new facility 

 in travelling. In some species the wings never become devel- 

 oped even in the adult ; but these are easily distinguished from 

 the immature stages of winged forms, because in the latter the 

 rudiments of the hind wings always cover those of the fore- 

 wings, while in adults, even when the wings are mere stumps, 

 the secondaries are always overlaid or covered by the others. 



Our best-known migrating forms belong to the genus Melan- 

 ophis, in which the anal extremity of the males is enlarged and 

 swollen. Here we find the Me/cmop/us spretiis, or "Rocky 

 Mountain locust," which in years past has caused ruin in many 

 States west of the Mississippi, and even yet does much injury 

 and periodically threatens disaster. The home of this species, 

 about which volumes have been written, is on the high, dry, 

 eastern slopes of the Rocky Mountains, and in some regions 

 west of these mountains in Idaho and Utah. There it breeds 

 abundantly each year, frequently extending into the adjacent 

 regions to obtain food and maintaining itself for some time. As 

 a result of any unusual increase in numbers with a corresponding 

 failure of food-supply, emigration may become necessary, and the 

 long, broad wings of the species suffice to carry it even to the 

 Mississippi River, ranging north and south from Minnesota to 

 Texas. But in these moist eastern regions the insect cannot 

 thrive, and from millions of eggs laid only a small proportion of 

 weakly larvae appear, which usually die before they mature. 



An allied but shorter-winged form is the Melanophis atlaiiis, 

 or "lesser locust," which occurs commonly over all the more 

 northern United States, while the M. fenmr-riibriim, or "red- 

 legged locust," is much the most common eastern species, some- 

 times doing considerable injury to crops. 



Among the more common short-winged forms we have in the 

 East species of Paroxya, in which the males are smaller and 

 ready fliers, the females much larger, with wings covering half 

 the abdomen, and used rather as aids in leaping than as organs 



