No. 6.] RILEY — ROCKY MOUNTAIN LOCUST. 365 



to call species are often with difficulty separated from each other ; 

 that they have, in fact, no real existence in nature. All our 

 classificatory divisions are more or less conventional. They are 

 excellent as aids to thought and study, but misleading when be- 

 lieved — as they popularly are — to express absolute creations that 

 have existed for all time. 



As with other species, so it is with the locust under considera- 

 tion. The species is a denizen of the plains regions of the 

 Rocky Mountains to the west and northwest of us. It breeds 

 continuously and comes to perfection only in those high and dry 

 plains and prairies; and though at intervals it overruns much of 

 the lower, moister country to the east and southeast, yet it never 

 extends in a general way to the Mississippi. But there are spe- 

 cies east of the Mississippi that are so closely allied to it that the 

 ordinary fanner cannot, without a little special knowledge, ap- 

 preciate the difference, and entomologists, even, are not of a 

 mind as to whether they should be called species, varieties, or 

 races, etc. The two species most closely allied to the Rocky 

 Mountain locust are the red-legged locust (Caloptenus femur- 

 rubrum) and the Atlantic locust (Caloptenus Atlantis). Both 

 are wide-spread species, but are either rare or do not occur in the 

 home of spretus. The differences between the three species I 

 have elsewhere given in detail ; for the present purpose it suffices 

 to say that the distinguishing characters, most easily observed 

 by the non-entomologist, are the relative length of the wing and 

 the structure of the terminal joint of the male abdomen. The 

 Rocky Mountain species has the wings extending, when elosed, 

 about one-third their length beyond the tip of the abdomen, and 

 the last or upturned joint of the abdomen narrowing like the 

 prow of a canoe, and notched or produced into two tubercles at 

 top. The wings of the red-legged locust extend, on an average, 

 about one-sixth their length beyond the tip of the abdomen, and 

 the last abdominal joint is shorter, broader, more squarely cut 

 off at top, without terminal tubercles, and looks more like the 

 stern of a barge. 



The Atlantic locust, though smaller than either, is in other 

 respects intermediate between the two, but in relative length of 

 wing and structure of the anal joint in the male, most related 

 to spretus. 



We should encourage the locust's natural enemies. Practically 

 this is not possible with many of the smaller parasitic and preda- 



