7 
without injury, and the chrysalid of the Large Cabbage 
Butterfly will develop properly after being exposed to a 
temperature of zero. 
Without, however, going into too minute details of the 
various experiments that have been recorded from the 
time of Reaumur onwards, it appears that these common 
farm-pests will survive, so long as they are in their own 
cells, a greater amount of cold than they will be exposed 
to, even if the temperature sank on the surface of the 
ground to zero for a much longer time than is likely to 
occur in the greater part of these islands. 
If they are not in their own cells circumstances will 
affect them very differently, for we find that with many 
of our caterpillars and chrysalids it is not the effect of 
cold alone that destroys them, but if (by ploughing, 
digging, or any other operations) we can throw them out 
of their cells, or other defences they have prepared for 
their winter habitations, and thus scatter them, mix 
them with the soil and expose them to drying winds, to 
alternate freezing and thawing, or lying soddening in the 
rain, or wet ground, when too torpid to move, that thus 
we get rid of great numbers. 
To put this in other words, as brought forward in one 
of the Reports of the State Entomologist of Illinois:— 
“It is evident that freezing does not injure the ‘ cut¬ 
worms ’ (as what we call surface-caterpillars are there 
described), for Nature has prepared them for it, ... . 
but freezing in connection with loose wet soil, and this 
will kill the chrysalids as quickly as it will the worm or 
caterpillar.” 
There are many other crop-attacks which may be 
checked by following up the same principle of disturbing 
the customary winter arrangements of the insect, and 
taking advantage of the short season in which winter 
torpidity throws these troubles of the summer into our 
power. Thus in the case of the maggots and pupae of 
some kinds of the Diptera (or two-winged flies) we may 
throw them on the surface, or turn them down so deeply 
in autumn cultivation that any flies that may develop 
