INTRODUCTION OF INSECTS. 135 
sian fly, Cecedomyia destructriz, made its appearance, and it 
was so called because it was first observed in the year when the 
Hessian troops were brought over, and was popularly supposed 
to have been accidentally imported by those unwelcome stran- 
gers. Other destroyers of cereal grains have since found their 
way across the Atlantic, and a noxious European aphis has first 
attacked the American wheatfields within the last fifteen years. 
Unhappily, in these cases of migration, the natural corrective 
of excessive multiplication, the parasitic or voracious enemy of 
the noxious insect, does not always accompany the wanderings 
of its prey, and the bane long precedes the antidote. Hence, 
in the United States, the ravages of imported insects injurious 
to cultivated crops, not being checked by the counteracting in- 
fluences which nature had provided to limit their devastations 
in the Old World, are more destructive than in Europe. It is 
not known that the wheat midge is preyed upon in America by 
any other insect, and in seasons favorable to it, it multiplies to 
a degree which would prove almost fatal to the entire harvest, 
were it not that, in the great territorial extent of the United 
States, there is room for such differences of soil and climate as, 
in a given year, to present in one State all the conditions favor- 
able to the increase of a particular insect, while in another, 
the natural influences are hostile to it. The only apparent 
remedy for this evil is, to balance the disproportionate develop- 
ment of noxious foreign species by bringing from their native 
country the tribes which prey upon them. This, it seems, has 
been attempted. The United States Census Report for 1860, 
p- 52, states that the New York Agricultural Society “has in- 
troduced into this country from abroad certain parasites which 
Providence has created to counteract the destructive powers of 
some of these depredators.” * 
This is, however, not the only purpose for which man has 
designedly introduced foreign forms of insect life. The eggs 
of the silkworm are known to have been brought from the far- 
* On parasitic and entomophagous insects, see a paper by Rondani referred 
to p. 119 ante. 
