4 
of the method of insect attack not being a matter of 
mysterious uncertainty. 
From the small size of insects and their very different 
appearance at different stages of their lives, and also 
from many of their operations being carried on out of 
sight of all but those who follow the clue given by the 
state of the injured crop, the fact that their lives are as 
much governed by laws as those of animals which from 
their larger size are more easily observable, is not so 
much thought of as it ought to be. 
If it was once settled in the mind that their propa¬ 
gation and their changes from one stage to another, the 
food they require, and the other methods of carrying on 
life were subject to rules, and when they altered that 
they varied with variations in surrounding circumstances, 
it would give a hopefulness to study, a certainty of 
benefit repaying investigation, that would be of much 
service. So long as there is vague uncertainty in the 
mind of an observer, how can he work with any comfort 
or confidence? But let him once be convinced by 
reasonable proof that the insect he is studying has a 
fixed method of life; that it will die of starvation if it 
has no food ; be cleared out by taking away its shelter ; 
that heat and sunshine, or cold and wet, have certain 
effects upon it; and he will, so to say, go at his work 
with a will, and he will prosper in it. 
The Life History of the Turnip Fly is well known, 
but for convenience of reference at present I give the 
main points as shortly as possible. 
The Fly, or more properly the Flea-beetles, live through 
the winter,—in a torpid state or otherwise, according to 
the amount of cold,—and under such shelter as is 
afforded only too often by rough ground, stones, or 
apparently almost any kind of moderately dry field 
rubbish. 
With the return of sunshine they come out to trouble 
us, and feed, until the Turnips and Cabbage are ready 
for them, on such wild plants of the Cabbage kind as 
they can find—as the common Shepherd’s Purse, the 
