156 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
CHAPTER VI. 
THE SOUTHERN LIMITS OF THE DISTRIBUTION OF THE 
ROCKY MOUNTAIN LOCUST. 
In view of the probable speedy completion of the Atchison, Topeka, 
and Santa F6 Railroad and the Southern Pacific Railroad, and the pro- 
jected lines of the Atlantic and Pacific, and Southern Pacific Railroads 
connecting the Pacific coast and Gulf States, as well as the lower valley 
of the Mississippi River, and thus opening up to settlement the arable 
lands of portions of New Mexico and Arizona, it has become of a good 
deal of practical importance to define with some degree of certainty the 
southern limits of the distribution of the Rocky Mountain locust. 
For this purpose we made a journey in the summer of 1879 to Santa 
Fe, N. Mex., and adjoining places, and were able to obtain much new 
information regarding the distribution of this locust in New Mexico and 
also to learn something of its occurrence in the adjoining Territory of 
Arizona. The facts collected have been embodied in the map accom- 
panying this report and in the pages farther on. 
It appears from our investigations that the permanent breeding 
grounds of the locust scarcely extend into New Mexico, and probably not 
at all into Arizona. The area, however, into which they periodically emi- 
grate from the permanent region embraces the northern half of New 
Mexico and the northeastern corner of Arizona, i. e., that portion adjacent 
to New Mexico and possibly to Utah. From this it appears that those 
portions of the valleys of the Pecos and Rio Grande Rivers lying in the 
northern two-thirds of the Territory of New Mexico are periodically in- 
vaded by the Rocky Mountain locust, the source of supply being the 
mountain valleys and parks of Southern and Southwestern Colorado. 
But it is most probable that the fertile valley of the Rio Grande lying 
south of Fort Craig, and most valuable as a wine-growing district, will 
never suffer from the invasions of this pest. 
To recapitulate what the Commission has been able to ascertain re- 
garding the southern limits of the locust region, we may say that in 
Texas it reaches, and is bounded on the south by, the Rio Grande ; in one 
year * the locusts having crossed the river and entered Mexican territory 
fer the distance of a mile or so. The species is apparently absent from 
Southern New Mexico and from Central and Southern Arizona, as well 
as from Southern Nevada ; unless it should eventually be found existing 
in limited numbers on the subalpine mountain peaks of these regions. 
There is every probability that the locust (Caloptenns spretus) will not 
be found in Lower California and the Peninsula of California, and that 
it does not inhabit Mexico. That this is the case seems probable from 
* 1873. See First Report of the Commission, pp. 59, 60. 
