INSECTS INJURIOUS TO THE POTATO. 95 
in attempting to breed the Maple Worm (Dryocampa rubi- 
cunda). The larva retires to some cool moist place beneath 
a board, stone, or anything it can find on the ground, where 
it will not be exposed to the dry atmosphere, for the chrysa- 
lis is naked. Now take this same chrysalis and put it into 
a dry box, and it most likely will perish, and fail to perfectly 
develop. Many lepidopterous larve protect themselves with 
an impervious cocoon where they are exposed to atmospherie 
vicissitudes. This, I believe, is not only to protect them 
from the rain, if it is at all for this purpose, as entomolo- 
gists often suppose, but to protect them from the far more 
injurious influence of evaporation during the long time they 
take no liquid nourishment. It is for this purpose also 
that the Cecidomyian larva cements its spun cocoon with a 
gummy fluid, as I have shown in the "Transactions of the 
American Entomological Society," for October, 1867. We 
therefore find here another example of climatic causes, pro- 
ducing disease and death among insects in a wholesale man- 
ner. 
Entomological writers usually represent cannibal insects 
as the most efficient means in nature for the extermination 
of injurious insects, and in the reports of State Entomolo- 
gists we occasionally find them speaking in glowing terms of 
the power that man can exert in cóntrolling injurious insects. 
While we may not despise these measures of protection, es- 
pecially the former—for without the Ichneumon fly, the Syr- 
phus fly, the Coccinelle, etc., we would doubtless be overrun 9 
by swarms of caterpillars, plant-lice, and other noxious depre- 
dators—let us not forget the great truth, that climatie 
. causes, producing death by epidemie diseases and various 
other means, are infinitely in advance of most other natural 
means of exterminating noxious insects (for my extended 
views and observations on this topic, see an address before 
the Northern Illinois Horticultural Society, and published 
in the first volume of the Transactions of that body, and my 
sport of a remarkable epidemic disease observed among 

