THE NEW MEXICO RANGE CATERPILLAR. 61 



east and continue to spread in these directions, or whether, owing to 

 the high altitude and consequent atmospheric and meteorological 

 conditions, it will be restricted to this particular section of the country. 



The character of the country covered by the present outbreak 

 should be mentioned here. Northeastern New Mexico consists 

 mainly of a high plateau 6,000 to 7,000 feet above sea level, inter- 

 spersed with mountainous masses that show evidence of volcanic 

 action in some remote time. The entire region — plains, valleys, and 

 even the "high mesas" 8,000 feet in altitude — is covered with a more 

 or less complete clothing of nutritious grasses (Plate III, fig. 1). 

 Little else will grow here. The systematic overstocking of the range 

 in years gone by has, however, partly eliminated these grasses and 

 allowed many worthless weeds like the sheepweed (Gutierrezia sp.) 

 and the Russian thistle (Salsola tragus) to dominate large areas, to 

 the detriment of the live-stock industry. The native grasses, such as 

 the grama (blue and black) and Agropyron, seldom perish entirely 

 from overstocking, but often afford only limited pasturage. Since 

 the range caterpillar has taken possession of this entire region, feeding 

 mainly on grama and buffalo grasses, the carrying capacity of the range 

 has been much reduced, and in places utterly ruined. Not only has 

 the grass been eaten to the very roots for miles at a stretch by these 

 " range worms" (Plate III, fig. 2) , but the uneaten grass in the infested 

 territory is not relished by stock on account of the trail of silk left 

 everywhere by the caterpillars, especially during the molting season. 



The first authentic history of the genus Hemileuca in New Mexico 

 begins about five or six years ago. In the year 1904 or 1905 a vast 

 horde of caterpillars appeared in destructive numbers in the vicinity 

 of Springer Lake, New Mexico, an irrigation reservoir a few miles from 

 Springer, a station on the Santa Fe Railway, 50 miles south of the 

 Colorado line. That section appears to have been the starting point 

 of the present outbreak, and from there it has spread north and east 

 and south, being checked on the west only by the foothills of the Taos 

 Mountain range. 



Whether or not this locality is the original home of this species, the 

 pest has become most thoroughly established everywhere on the great 

 rolling stretches of grazing land where it is now found. Even the 

 weeds of the region, mostly adventitious, combine with the native 

 grasses to make existence possible for the pests by affording shelter 

 from the heat of the midday sun, support for molting, and, later, for 

 pupation. Indeed it seems doubtful if this species could easily sur- 

 vive under the conditions that prevailed before the introduction of 

 weeds, at least on the level plains. 



But the Hemileuca is by no means confined to the broad, low-lying 

 mesas. In August, 1909, a large colony of full-grown larvae was 

 discovered in a natural grama-grass meadow on the summit of one of 



