INFLUENCE OF WEATHER ON THE SPECIES. 423 



Bat on Professor Lapham's hypothesis there would naturally bo a con- 

 nection in the past between fires and locusts; for if, without fires, this 

 whole prairie region had been timbered, the locusts, which are essen- 

 tially insects of the plains and prairies, could never have become so 

 prodigiously abundant and injurious. On such a hypothesis alone can 

 we see any possible connection between prairie-fires and locust invasions; 

 and, however much truth there may be in the hypothesis, the fact 

 remains that there is no present connection between the two phe- 

 nomena." 



CHAPTER XV. 



INFLUENCE OF WEATHEE ON THE SPEjGIES. 



Although we cannot doubt that the climate of the Eocky Mountain 

 region and of the plains where the Eocky Mountain locust dwells, de- 

 termines largely its characteristics, habits, and destructiveness, yet the 

 want of accurate simultaneous observations from numerous points still 

 prevents us from entering into that systematic investigation of the sub- 

 ject that would thoroughly elucidate such questions as are still obscure. 



On the one hand, we know from observation in a general way (1) 

 that the species comes to perfection in what we have (Map I) designated 

 as the Permanent region, which is elevated from one to four thousand 

 feet above the sea ; (2) that it migrates by flights, to some extent west- 

 ward, but especially eastward to Manitoba and southward to Texas, 

 rarely passing the 94th meridian on the east or to within fifty miles of 

 the Gulf of Mexico on the south; (3) that the progeny born in these 

 low lands return, as far as they are able, to the higher regions near the 

 birthplace of their ancestors. 



On the other hand, we consider that the meteorological conditions 

 affecting their life most probably are: (1) The temperature of the soil 

 in which the eggs are deposited ; (2) The indirect effect of climate by 

 its influence on the condition of the young grasses and plants at the 

 time of hatching of the young and up to the period of the insect's ac- 

 quiring wings ; (3) The temperature, rain-fall, and dryness at the sur- 

 face of the ground during the unfledged condition of the young locust; 

 (4) The winds and weather prevailing when the insect is ready to mi- 

 grate ; (5) The nature of the vegetation, soil, and climate in the re- 

 gion to which it migrates and where the eggs are to be laid. 



With respect to migrations, the meteorological bcaiings on them 

 have been considered in Chapter VII; the other vital questions in re- 

 gard to the increase and the perpetuity of the species, and therefore in 

 regard to its permanent destructiveness, relate to the conditions to 

 which the eggs and the young insects are subjected, and will be consid- 

 ered in the present chapter. 



