POOL EIN WS Ta 
INSECTS AFFECTING DOMESTIC ANIMALS. 
CHAPTER I. 
INTRODUCTION. 
DEFINITIONS AND ARRANGEMENT. 
The relations which insects bear to the other branches of the animal 
kingdom are of no little complexity, and the complete statement of 
these relations would require a lengthy discussion of definitions. 
In the present work it is intended to discuss particularly those 
insects which by direct attack upon domesticated animals render them- 
selves an injurious element to the stock breeder, poultry raiser, and 
keeper of various animals for pleasure or profit. Naturally, reference 
must here and there be made to allied forms which may be of interest 
as affecting some related animals or as possible parasites of domestic 
animals in the future. 
_ Insects may affect domestic animals in a number of different ways; 
first, by occasional attack for the purpose of obtaining food; second, 
by occasional attacks which simply give irritation to the animal, as in 
the case of certain species of flies; third, by living as parasites during 
part of their existence, as in bots; fourth, by living as parasites 
throughout their lifetime, as with the lice; and, fifth, by living as mess 
mates or scavengers upon the bodies of the animals without deriving 
nutriment from them, as, probably, some species of bird lice. 
In general, the insects affecting animals are termed parasites, but 
evidently this term would not be appropriate for all the forms above 
mentioned. It is by no means easy to give a definition which shall be 
properly exclusive. 
We may say that a parasite is an animal which lives at the expense 
of another, but this would not include many species which are com- 
monly considered as parasites and which, while dependent upon a host 
animal for existence, take nothing that is of value to the host. On 
the other hand, if we say the parasite is an animal dependent at some 
period of its life upon another for existence, we must include many 
forms which have none of the habits which we commonly associate 
with parasitism. 
Van Beneden has proposed three groups—parasites, messmates, and 
mutualists. In the first group are placed all those forms which feed 
upon the tissues of the host. In the second group are placed those 
which simply take the food collected by the host, but do not demand its 
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