17 
certain amount of regular bird presence should be 
scrupulously kept up, including some of the twilight 
flyers, as the Nightjar, and others, which help us 
regarding injurious Moths ; but with regard to establish¬ 
ing colonies of birds, it may be doubted whether there 
are many so purely insectivorous or animal feeders as 
not to make it a great risk that if insect-food fails they 
will be infinitely worse for the crop. Also it is not 
always borne in mind that one great natural protection 
we have from injurious excess lies in the insect parasites, 
the Ichneumon, and other kinds of parasitic flies, and 
that the insectivorous bird will destroy alike our insect 
pest and our insect helper. 
Weather influences do not act quite similarly on all 
kinds of insects, and these effects are very important, 
for, although we cannot as yet forecast weather reliably 
enough for agricultural purposes, we can very reliably 
forecast some kinds of insect-attack from certain states 
of the weather joined to their effects on plant-life and on 
the condition of the ground ; also we can modify weather 
effects by agricultural operations, amongst others by 
such drainage and arrangement of field ponds and 
cisterns as would enable us in some degree to store the 
surplus rainfall of one season to meet the deficiencies of 
the next. Some insects, such as the Tipidce, commonly 
known as the Daddy Long-legs or Crane Fly, may surely 
be expected (unless proper measures are taken) in greater 
numbers after wet seasons ; the damp ground and pro¬ 
tection of the damp leafage suit them best for ovi- 
position and development; their larvae will bear con¬ 
tinuous immersion in water for about fifty-eight hours 
without being destroyed, and it was found, in an experi¬ 
ment kindly tried for me by Mr. Whipple, at Kew 
Observatory, that they would exceptionally bear a tem¬ 
perature of ten degrees below zero, that is forty-two 
degrees of frost. There is a widespread idea that a 
severe winter is a great help to us by clearing off cater¬ 
pillars, maggots, and insects generally, but, so far as 
observations go at present, this is very far from being 
B 
