ORTHOPTERA. 



201 



FIG. 281. Caloptenus spretus. Rocky Mountain locust, 

 in flight. 



joint, so that during the process they were doubled throughout their length. They 

 were as supple at the time as an oil-soaked string, and for some time after extrication 

 they show the effects of this severe bending by their curved appearance. 



" The moulting, from the bursting of the pupa-skin to the full adjustment of the 

 wings and straightening of the legs of the perfect insect, occupies less than three- 

 quarters of an hour, and sometimes but 

 half an hour. It takes place most fre- 

 quently during the warmer part of the 

 morning, and within an hour after the 

 wings are once in position the parts have 

 become sufficiently dry and stiffened to 

 enable the insect to move about with 

 ease ; and in another hour, with appe- 

 tite sharpened by long fast, it joins its 

 voracious comrades and tries its new 

 jaws. The moulting period, especially the 

 last, is a very critical one, and during the 

 helplessness that belongs to it the unfor- 

 tunate locust falls a prey to many enemies 

 which otherwise would not molest it, and 

 not infrequently to the voracity of the more active individuals of its own species." 



This species continue to exist year after year for an indefinite period only under 

 certain conditions, and hence is a more permanent resident of one section of the coun- 

 try than of another. These peculiar conditions obtain in the great Northwest where the 

 country spreads out into vast treeless plains that have a comparatively high elevation 

 and are dry. 



There have been various theories advanced as to the cause of the migratory 

 movements of this locust, but we should not look to any one, but to several causes that 

 may either singly or combinedly produce the result. Were we asked for any single 

 explanation or predisposing cause, w r e should answer, Excessive Multiplication; for 

 the others are mostly secondary, or but consequences of this one. Among these may 

 be enumerated hunger, the procreative instinct, annoyance by natural enemies, and 

 possibly a true migratory instinct. In its flight the species frequently travels as fast 

 as from twenty to thirty miles an hour, and single swarms have been traced over a 

 stretch of country many hundreds of miles in length. 



The genus Pezotettix, which is represented in this country by about thirty recog- 

 nized species, differs from the preceding genus only in the abbreviation of the elytra 

 and wings. Many of the species of Caloptenus have representatives in Pezotettix, the 

 correspondences in all other respects being so close that it is difficult to decide whether 

 the one should be considered merely a short-winged form of the other or whether it 

 represents a permanent and distinctive type, and these facts indicate that Pezotettix, 

 considered as a genus, has had its origin in arrested wing development of Caloptenus. 

 The species of Pezotettix are, however, more localized in distribution and often chiefly 

 confine their diet to a single or a special group of plants. They are, like the Calop- 

 teni, partial to cool or shady localities, and hence are most frequently to be met with 

 where vegetation is somewhat rank, as along the margins of streams and groves. They 

 are also more fi-equent in mountainous than in level countries. Pezotettix alba, a 

 greenish-white species, is found in Nebraska, where it lives solely upon a plant known 



