248 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



west Territory. In 1875 the locusts hatched out in immense numbers, 

 and utterly destroyed the crops in the province of Manitoba. Now, in 

 1876, they were very numerous over all the third prairie steppe of British 

 America, and largely went to make up the autumn swarms that came 

 into our own country that year. Governor Morris started late in July 

 of 1870 from Winnipeg northwest to make a treaty with certain Indians, 

 and during the first five or six days of August he encountered innumer- 

 able locust swarms all the way from the forks of the two main trails to 

 Fort Ellice. The wind was blowing strong from the west all the time — 

 Just the very direction to carry the insects straight over into Manitoba. 

 The governor watched their movements with the greatest anxiety, fear- 

 ing that the .Province would again be devastated as it had been the 

 previous year. Yet, during all the time he was passing through the 

 immense swarms, they bore doggedly to the south and southeast, either 

 tacking against the wind or keeping to the ground when unable to do 

 so. I^othing was more remarkable than the manner in which they per- 

 sisted in refusing to be carried into Manitoba. A few were blown over, 

 but did not alight, and the Province seemed miraculously delivered. 

 Mr. Whitman tells us, again, that in settling in 1877 the insects avoided 

 those counties in Minnesota in which they had hatched most numerously 

 and done greatest injury, but selected such as had not suffered for some 

 years past. 



We are inclined to believe that there is more than mere coincidence 

 in these occurrences, and will venture to offer what appears to us a 

 plausible explanation of them. In treating of the natural enemies of 

 this locust, we shall presently show that the mature insects are seriously 

 affected by a little six-legged mite, and that the eggs are preyed upon 

 by another and larger eight-legged mite. We have long believed that 

 the former was the young of the latter; but only the present year, by 

 breeding hundreds from the egg to the mature condition, and studying 

 these mites in all their transformations, have we been able to demon- 

 strate the fact. (See Chap. XI.) 



The life-history of this little animal, differing so much in its infancy 

 and maturity that naturalists have classed it in two distinct genera, has 

 much belonging to it of purely scientific interest; but how much more 

 interesting does it now become to our Western farmers! Every careful 

 observer knows how generally the locusts, whenever they abound un- 

 precedentedly, are infested with and debilitated by the little red mites 

 under the wings. Let us imagine those mites dropping by dozens from 

 every locust throughout a given region that is being ravaged, each mite 

 lying in wait to presently pounce, in altered form, upon any locust eggs 

 that it can find ; and we cease to wonder that Caloptenus spretus quits 

 such a country whenever its wings have become strong enough to enable 

 it to do so, or that flying swarms avoid such localities in descending to 

 oviposit. We may wonder at the instinct that guides them, but no 

 more than we must ever wonder at the many to us equally incompre- 



