THE SPECIES ESSENTIALLY SINGLE-BROODED. 241 



much experience, and his opinion deserves consideration. The question 

 can also be best discussed in reply to such an argument : 



Glencoe, Dodge County, Nebraska, 



October 18, 1877. 



Dear Sir : I have frequently taken occasion to express, through the medium of 

 various publications, my belief in the double-brooded character of the Rocky Moiintaiu 

 locust, and during several years' experience with this insect I have seen no good reason 

 for changing my opinion. 



It is an undisputed fact that instinct in insects is chiefly displayed in providing for 

 the reproduction of the species. Why should this not be the case with our locust ? It 

 is plain that the locust is guided by instinct in its migrations, from the following facts, 

 which I can substantiate by my own notes and those of other observers. 



1. The migrating locust always leaves its breeding-grounds as soon as it has gained 

 sufficient strength to take long flights, providing it is not delayed by storms or con- 

 trary winds. That this movement is nofc made on account of hunger is shown by the 

 fact that it passes over large tracts of luxuriant vegetation without alighting, and when 

 obliged to stop for rest or food, immediately resumes its flight if wind and weather 

 continue favorable. An instance is seen in the conduct of those hatched in Missouri 

 in 1875, which flew away to the northwest, leaving almost untouched the growing 

 crops of the border States. 



2. They fly north in the first part of the season, and south in the latter part, and no 

 amount of adverse weather can turn them back on their course. 



When flying north they go indifferently with a southeast or southwest wind, and 

 vice versa when flying south ; but a head wind always brings them down, and however 

 g"eat their apparent anxiety to move on, they invariably wait for a wind that will 

 bear them upon the same general course that they first took. A distinction must here 

 be made between their flight when migrating and their movements in search of food. 

 During the latter, they fly near the ground to any point of the compass, frequently making 

 a simultaneous movement over large areas. But this is not migrating, although it un- 

 doubtedly occasions many of the conflicting reports that annually appear in regard to 

 their course of travel. The habit of waiting for a favorable wind must have been 

 observed by all who have seen the locust on its travels, and it shows that its course of 

 migration is governed by fixed rules, wholly independent of the prevailing winds, ex- 

 cept as they may serve to bear it toward the desired point. 



Taking any given year, I find that winged locusts begin to arrive here in May (in one 

 instance as early as May 12) and continue to pass over from the south until the middle 

 or latter part of July. They begin arriving from the north sometimes as early as July 

 1, and continue to fly over at intervals until late in autumn. 



In 1873, one of these southern swarms, being compelled to alight here by rainy 

 weather in May, deposited many eggs, which hat: hed in June of the same season. The 

 young became full-fledged and flew south about the middle of August. It is evident 

 that the parent swarm was hatched that spring in the north ; and the fact that a sec- 

 ond brood w^as produced from their eggs that season shows that the species is double- 

 brooded under favorable conditions. Such conditicns are obtained by the habit of 

 migrating from a southern to a northern climate. 



If the swarm that halted here had continued its flight with favorable weather hun- 

 dreds of miles farther north, the second brood would have been produced just the same. 



Every year, as all observers know, immense swarms go north in the spring, and I do 

 not doubt that their progeny, reared upon the tender pasturage of the north, constitute 

 the swarms that annually move south in the late summer and fall. 



Probably the annual migratory movements are performed upon the plains with more 



regularity than in the Mississippi Valley, where storms and changeable winds serve to 



impede their progress. It may not be possible for this species to invariably mature two 



broods in one season, and in that case nature may have provided for the lireservatiou 



16 G 



