372 ROCKY MOUNTAIN LOCUST yond the tip of the abdomen), and the last abdominal joint of the male is bluntly cut off at the top, and not tapering and notched as in Fio. 8. Anal Characters of Male of Kocky Mountain Locust: a, side view of tip; b, o, hind and top views. FIG. 4. Anal Characters of Male of Red-legged Lo- cust : a, side view of tip; t>, c, hind and top views. spretiu. There is a third species, ealoptenut Atlantis (Riley), occurring more particularly in the mountain regicfhs of the Atlantic, which in many respects is intermediate between the two, and which often migrates in large swarms from place to place, and proves injurious du- ring very hot dry years. All three approach each other so closely through divergent indi- viduals that entomologists are at variance as to whether they should be considered distinct species, or mere varieties or geographical races of the same species. But compared with the Rocky mountain species, the others are harm- less. This species seems to be subalpine by nature, and to breed and flourish only in the high plains and plateaus of the Rocky moun- tain region ; and Prof. C. V. Riley is of opin- ion that those which devastate 8. W. Dakota, Nebraska, Kansas, and the western portions of Minnesota, Iowa, and Missouri (in all of which country the species is not indigenous), come principally from the mountain regions of Wyoming, Dakota, Montana, and British America. According to his seventh annual " Report on the Insects of Missouri," " the in- sect is at home in the higher altitudes of Utah, Idaho, Colorado, Wyoming, Montana, N. W. Dakota, and British America. It breeds in all this region, but particularly on the vast hot and dry plains and plateaus of the last named terri- tories and on the plains W. of the mountains ; its range being bounded, perhaps, on the east by that of the buffalo grass. William N. Byers of Denver, Colorado, shows that they hatch in immense numbers in the valleys of the three forks of the Missouri river and along the Yel- lowstone, and how they move on from there, when fledged, in a S. E. direction at about 10 m. a day. The swarms of 1867 were traced, as he states, from their hatching grounds in W. Dakota and Montana, along the E. flank of the Rocky mountains, in the valleys and plains of the Black hills, and between them and the main Rocky mountain range. (See Hayden's "Geological Survey of the Territories," 1870, pp. 282-'3.) In all this stretch of country, as is well known, there are vast tracts of barren, almost desert land, while other tracts for hun- dreds of miles bear only a scanty vegetation, the short buffalo grass of the more fertile prai- ries giving way, now to a more luxurious vege- tation along the watercourses, now to the sage bush and a few cacti. Another physical pe- culiarity is found in the fact that while the spring on these plains often opens as early, even away up into British America, as it does with us in the latitude of St. Louis, yet the vegeta- tion is often dried and actually burned out be- fore the first of July, so that not a green thing is to be found. Our Rocky mountain locust, therefore, hatching out in untold myriads in the hot sandy plains, 5,000 or 6,000 ft. above the sea level, will often perish in immense numbers if the scant vegetation of its native home dries up before it acquires wings ; but if the season is propitious and the insect becomes fledged before its food supply is exhausted, the newly acquired wings prove its salvation. It may also become periodically so prodigiously multiplied in its native breeding place that, even in favorable seasons, everything green is devoured by the time it becomes winged. In either case, prompted by hunger, it rises in vast clouds in the air to seek for fresh pas- tures. Borne along by the prevailing winds that sweep over these treeless plains from the northwest, often at the rate of 60 or 60 m. an hour, the darkening locust clouds are soon car- ried into the more moist and fertile country to the southeast, where they fall upon the crops like a plague and a blight. Many of the more feeble or of the more recently fledged perish, no doubt, on the way; but the main army succeeds, with favorable wind, in bridg- ing over the parched country which offers no nourishment. The hotter and drier the season, and the greater the extent of the drought, the earlier will they be prompted to migrate, and the further will they push on to the east and south." These vast flights never extend E. of a line drawn at a rough estimate along the 94th meridian ; nor do they remain permanent- ly in the low Mississippi valley country. The sudden change from the attenuated and dry atmosphere and general climatic conditions of 5,000 or 6,000 ft. above the sea, to the more humid and dense atmosphere of 1,000 ft., affects them injuriously, and they either leave, die, or disappear through degeneration or miscegena- tion, until no trace of them is left by the sec- ond or third generation. These incursions into the more fertile country to the east occur at irregular intervals, and are most frequent in the country toward the northwest, nearest the native home of the species. Thus, locust rav- ages are more to be feared in Colorado and W. Minnesota than in Missouri or Texas. A chronological study of these incursions shows that there have been during the present cen- tury only three as extended as that of 1874, when the insects reached into the western counties of Missouri. But we find records of a dire visitation in Guatemala as far back as 1632, in Gage's "West Indies," and the early Jesuit missionaries of California have left nu- merous records of locust injuries on the Pa- cific coast during the present and preceding
