Home, and Range East of Mountains. 67 



that they may not to some extent spread beyond that line, 

 in years to come, or that the young, hatching from invad- 

 ing swarms may not exceptionally push beyond it ; for I 

 have numerous records to show that the insects have 

 occurred as far as the western point of Lake Superior, and 

 that they have even reached the Mississippi in parts of 

 Iowa : but in all such instances they appeared in scatter- 

 ing numbers only, and did no material damage. They 

 ^ere the last remnants of the mighty armies from the 

 mountains, moving and blowing about, diseased, parasit- 

 ized, intestate and wasting away. 



It is an interesting fact, as shown by the distribution of 

 timber in the United States, that this limit-line follows, in 

 the main, the separation of the timber from the plains and 

 prairie regions, or, more correctly speaking, the line which 

 separates that vast region between the Mississippi and the 

 mountains in which the timber averages not more than 

 «ix or seven out of every one hundred acres, and that in 

 which it averages twenty-five or thirty out of every one 

 hundred. In this fact we also get another probable ex- 

 planation of the eastern limit of injury by spretus. 



Well is it for the people of the Mississippi Valley that 

 this insect can not go on multiplying indefinitely in their 

 fertile fields ! Else, did it go on multiplying and thriving 

 as the Colorado Potato-beetle has done, this whole valley 

 would soon become a desert waste. 



It will be a source of satisfaction to the farmers east of 

 the line indicated (however little it may be to those on 

 the westward side,) to feel assured against any future inva- 

 sion by, or any serious injury from, an army of insects so 

 prodigiously numerous as actually to obscure the light of 

 the sun, and so ruinously destructive as to devour almost 

 every green thing that grows ! 



