f 



31 



ance of the army worm and grain aphis, were unusually warm and dry, and favourable 

 not only for the hatching of the eggs laid the year previous, but for the growth and deve- 

 lopment of the larva? or young. Look now at the conditions for the development of 

 locust life on the hot and dry plains, chiefly of Dakota, Montana, Wyoming, and Idaho. 

 We have no meteorological records from these regions at hand, but it is more than prob- 

 able that the years preceding the migrations of the locusts were exceptionally warm and 

 dry, when the soil was parched with long-sustained droughts, as we know that the cor- 

 -responding species east of the Mississippi River abounds during dry summers following 

 dry and warm springs. 



" Given, then, the exceptional years of drought and heat and the great extent of ter- 

 ritory, and we have as the result vast numbers of young hatched out. The year previous 

 having, perhaps, been warm and dry, the locusts would abound, and more eggs than usual 

 would belaid. These would, with remarkably few exceptions, hatch, and the young soon 

 consume the buffalo grass and other herbage, and move about from one region to another, 

 following often a determinate course in search of food. In this way large broods may 

 migrate a long distance, from perhaps twenty to fifty miles. In about six or seven weeks 

 they acquire wings. Experience shows that the western locust, as soon as it is fledged, 

 rises up high in the air, sometimes a thousand feet or much higher. They have been seen 

 to settle at night on the ground, eat during this time, and towards noon the next day fill 

 the air again with their glistening wings. As more and more become fledged, the vast 

 swarm e.xhausts the supply of food, and when the hosts are finally marshalled, new swarms 

 joining perhaps the original one, the whole swarm, possibly hundred of miles in extent, 

 begins to fly oft', borne by the prevailing westerly and north-westerly winds, in a general 

 easterly and south easterly course. 



" (2.) Tfu; secniulary cause of the migration is the desire for food, and possibly the reproduc- 

 tive instinct. The fact that in their migrations the locusts often seem to select cultivated 

 tracts, rapidly cross the treeless, barren plain.s, and linger and die on the prairies and 

 western edge of the fertile valleys of the Missouri and Mississippi, indicate that the impell- 

 ing force is due primarily to the want of food, and that the guiding force is the direction 

 of the prevailing winds, for they have no leaders, and we do not believe in the existence 

 of a " migratory instinct " in the locust any more than in the grass army worm, or the 

 cotton army worm, which it is sufficiently evident migrate from field to field, simply in 

 search of more abundant food. Meanwhile the reproductive system of the locusts is 

 maturing, the eggs ripening, and the uneasiness of the locusts during the course of their 

 travels may be unconsciously stimulated by the sexual instincts and the desire to discover 

 .suitable places for egg-laying — a long and tedious operation. 



" It has been sufficiently shown that a swarm of locusts observed by Professor Robin- 

 son near the entrance to Boulder Canon, Colorado, travelled a distance of about six hun- 

 dred miles to Eastern Kansas and Missouri. Though the .swarm wa.s first observed at 

 some distance north of Denver, Colorado, it was then on its way from the north, and may 

 have come from some part of Wyoming two or tliree hundred miles north-westward or 

 northward. Though the winds may vary, an<l counter-currents exist, and storm gusts 

 from due north, such as often sweep over the plains, and local southerly breezes may 

 retard their flight, the course is either eastward or south-easterly. We know enough of 

 the winds in the Western States and Territories to lay down the law that the general 

 direction of the winds in July and August, along the eastern slope of the Rocky Moun- 

 tains and on the plains, is from the west and north-west, and accords with the eastward 

 course of the locust swarms. The relations between the average direction of the winds 

 and the migrations of the locust have, however, never been sufficiently studied, either, so 

 far as we are aware, in Europe or in this country. And yet, if wo would intelligently 

 study the causes of the excessive increase and migrations of the locust, we must examine 

 the meteorological features of the country, ascertain the periods of drought and undue 

 rainfall, the average direction of the wind for the difl'ereiit montiis, in order to learn 

 how far they correspond with the phenomena of insect life. That there are meteorolo- 

 gical cycles, dry and hot seasons recurring at irregular intervals, wliile the general ave- 

 rage may remain nearly the same century after century, is supported, though it may 

 be vaguely, by observed meteorological facts. 



