18 
the case. Larvae of various kinds and chrysalids of 
Cabbage Butterflies have been exposed to cold that froze 
them hard, but on thawing appeared perfectly uninjured; 
the chrysalids developed in due time, and, as I found in 
the following year a small patch in my garden infested 
by the Black Weevils {Otio7^hynchus sulcatus), where 
I had never been troubled by them before, I conjectured 
that the experimental larvae of this species also were as 
uninjured as they appeared! Instances have been 
recorded showing that insects will bear a much lower 
temperature than they are likely to be exposed to in this 
country, but nevertheless they feel it. A sharp frost 
early in autumn will have a good effect in clearing Saw- 
fly caterpillars from trees in Pine plantations, and some 
of the ground-living larvae will go deep down in winter 
or during severe cold. Wireworms will go as much as 
a foot down. Cockchafer grubs will go down as much as 
two feet or more, and at these depths they rarely have to 
encounter a cold much below freezing-point. During the 
last winter, at my own climatological station at Isleworth 
(where the minimum thermometer on grass read as low 
as between two and nine degrees on several nights 
after the 20th of January), the temperature at one foot 
below the surface did not sink below 31 deg., and that 
at two feet not below 34 deg. This habit of some larvae 
of burying themselves is important agriculturally, as it 
may be that in consequence, ploughing, or paring, or 
operations especially meant to clear an infested field, 
may pass harmlessly above the spots where they lie 
buried for awhile. 
Generally speaking, sunshine and warmth appear to 
be the most favourable conditions for insect increase in 
this country during the months in which they are active. 
The parent insects are more lively and vigorous under 
such circumstances, and their longer flights in sunshine 
than in dull rainy weather spreads the attack over a 
larger extent of country, a larger proportion of the eggs 
appear to hatch, and the larvse to thrive better on plants 
with their sap matured by sunshine than on the watery 
