6 
INTRODUCTION. 
uninhabitable to any form of life inimical to them ; an organised cam¬ 
paign of the common black ant (Camponotus compressus) could effect a 
great deal and human methods of warfare would require to be revo¬ 
lutionised to deal with it. 
In practice we can consider insects as consisting of organisms whose 
actions will be definite responses to stimuli, whose movements and acti¬ 
vities will, under the same circumstances, be the same ; given the same 
conditions, all the individuals of a species will behave alike with only 
very minute variations which we have great difficulty in seeing. If we 
find that one of a species has a certain definite life history we are safe in 
concluding that under the same circumstances all of that species will 
have the same life history and that with a given departure from normal 
circumstances all will behave alike ; when we have worked out the life 
history and habits of one of a species, we can confidently assert that all 
will have that life history, with only small variations due to changed 
conditions ; a leaf-eating caterpillar that feeds on maize leaf in Behar, 
might quite well feed on juari leaf in Gujarat where maize is not grown, 
but it would not, for instance, become a borer in the Punjab and a pre¬ 
daceous caterpillar in Madras. We may, therefore, treat a species as an 
individual, and not expect to find different habits in different indivi¬ 
duals of the same species. At the same time we must allow for the 
variation consequent on changed conditions; the limit of adaptation to 
changed conditions is a very variable one ; as an example, many cater¬ 
pillars have but a very few foodplants and cannot live on others ; a few 
have many, and the Gram Caterpillar (Chloridea obsoleta) feeds on the 
seeds of gram, the heads of opium poppy, the heads of bajra or sunflower 
and a variety of other plants ; in the United States it is the boll worm 
feeding on the seed of cotton and accordingly has slightly different habits ; 
in this there is a certain amount of variation in habits due to changed 
foodplants. Such cases are frequent, but the variety of habits lies with¬ 
in perfectly clear and definite limits, varying slightly from species to 
species. On the above reasoning, a species is definable not only on 
structural characters but also on its habits and mode of life; if we look 
on a species as composed of individuals reacting mechanically to stimuli, 
with a limited play of adaptation to changing conditions, habits and 
mode of life are as much specific characters as is structure ; if our struc¬ 
tural distinctions are sound, they will be in agreement with habits and 
