654 REPORT UNITED STATES GEOLOGICAL SURVEY. 



de Borre, in the Coiaptr. Kendus of the Entomological Society of Bel- 

 gium, 1871-72, p. xviii : 



The migratory locust is au Orlhopin- peculiar to the torrid zone and a large part of 

 the north temperate zone of the Old World ; but, iu this last region, its northern limits 

 is subject to some variations, the explanation of which is one of the principal objects 

 of the work of M. Ko[)pen. 



In countries such as those of Arabia and Persia, where the mean temperature of the 

 .year, as that of the different seasons, is almost invariable, the abundance of the species 

 in question does not vary ; it is normally liruiied, both by the quantity of its nourish- 

 meut and the natural enemies of the insect. But this is not the case iu those countries 

 which, like Southern Russia, may present, sometimes favorable seasons, sometimes 

 years, or even simply seasons, unfavorable to the multiplication of Pachytiilus. Thus, 

 according to M. Koppen, the persistent prolongation of dry heat during a part of the 

 autumn will exert au influence on the quantity of eggs laid in favorable places ; and, 

 on the other hand, a temperature less than 14'^ R^aumer, [6H^° Fahr.,] prolonged for 

 several days toward the end of May, will be indispensable fo the hatching of the larva. 

 There would result from the more or less perfect realization of these conditions, and. 

 their succession or their interruption during several years, those dilferences observed 

 iu the northern limit of the species, which alternately increase or diminish the area oi 

 distribution. 



M. Koppen has distinguished and traced quite completely on the map for Europe 

 and Siberia three different limits of the geographical arenof PachijIylKS m'ujraloriua : L 

 The limits of its permanent distribution. 2. The limit of its temporary existence in all 

 stages of development, a little more to the north. Finally, 3. The limits of its presence 

 in the condition of bands of winged insects of a stated age, out of tlie regions where 

 the species may live and propagate. It will be necessary still to establish the limits of 

 accidental individual appearances, but that would be of questionable im)>ortance. The 

 northern limit of thi' permanent geographical distribution <vf Pachf/lijlns mi/jratoriua 

 begins iu Western Europe, from the coast of Portugal, near 40*^ latitude north, and ex- 

 tends fron) there toward the northeast as far as the month of the Bidassoa, thus leaving 

 out all tlie northwest portion of Spain; it continues to rise obliquely in France upas 

 far north as the lake of Geneva, and extends east, following more or less the lorty- 

 eighth degree of latitude, and embracing Valois, all of the north of Italy, Carinthia, 

 and Hungary, it passes into Southern Russia, where it attains nearly the fii'tieih de- 

 gree, passes likewise across the middle of Siberia, whence it passes over the north of 

 China, to end in Japan, at a latitude a little inferior to that of its point of departure 

 iu Portugal, leaving out the island of Niphou. M. Koppen remarks that all this limit 

 does not deviate much from the isothermaof 16° R. \_(JH° Fahr.] for the month of June. 

 To farther circumscribe the area, so extensive, of this species, the line goes from Japan 

 to the islands of Fidochi, to New Zealand and Australia, of which it only embraces 

 the northern parts, passes from there to the island of Mauritius, then rises to the 

 north, crosses Africa up to Madeira. But in this last part of the passage the limits are 

 more bypoti etical, from want of an exact knowledge of the existence of the si^ecies in 

 the interior of Africa. 



W^heu, in a country comprised in this area, as has "been frequently observed in 

 Southern Russia, the locusts develop in a certain abundance, the want of food obliges 

 them to migrate iu part in different directions, and to break over their limits. If cir- 

 cumstances ))erniit these emigrants to multiply for a certain period beyond their nor- 

 mal area, there results a temporary extension of this area, and occasionally new mi- 

 grations to the north, until only a single spring, colder or morehnnnd, comes lo ptit an 

 end to their invasion and to oblige tbem to go back to their natural limits. Tempo- 

 rary extensions like this of the area of distribution of Pachi/tyhts mifiratorius took 

 place in 1746 to 1749, and iu 1822 lo 1828 ; at these periods they appeared in Germany, 

 and ha%^e multiplied themselves during several successive years. The norihern- limit 

 of these temporary extensions may be also marked on the chart by a line which, tak- 

 ing its jjoint of departure iu the southwestern portion of Bavaria (where the Pachyty- 

 hts viigralorius has been observed from 1333 to 1339, and from 1748 to 1749), rises to 

 the northeast by Jena and Halle toward JClterbogk and Berlin, when it takes a nearly 

 eastern course, following more or less the parallel of 52|°of latitude, near Miiucheberg, 

 Kiistrin, Birnbaum, and Posen (regions which the species was known to have visited in 

 1730, 17.52, and from 1827 to 1828) ; then the line passes across Southern Poland, at the 

 fifty-second parallel, through the southern part of the government of t he MohiJew, inclin- 

 ing gradually toward the south, and extending so as to reach the AVolga and the Ural. 

 It is apparently to the humidity of the climate, injniious to the locust, likewise to the 

 state of the eggs during the winter, that we should attribute the less extension ot 

 this limit toward the north in Western Europe. 



To the north of the limits which have just been indicated, the Pac7iy/i/?«s jn?<;rafanM« 

 has not the power of undergoing its whole cycle of metamorphoses, neither, conse- 

 quently, to reproduce itself. This does not prevent its occasional appearance iu swarms 



