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14 INSECTS AFFECTING DOMESTIC ANIMALS. 
insects proper by the presence of four pairs of legs and are represented 
by the familiar spiders, ticks, mites, scorpions, ete. The parasitic 
forms, however, are included in the order Acarina, and in this order 
are confined to the families Trombidiide, Gamaside, Ixodide, and 
Acaride, the latter including the specially parasitic subfamily Sarcop- 
tine. The first family can scarcely be called parasitic, the species 
living on vegetation, but occasionally attaching themselves to animals 
and causing intense suffering. The Ixodide also breed upon vegeta- 
tion, but depend upon attaching themselves to mammals in the later 
stages of their development, and with some, at least, this seems essen- 
tial in the maturity of the reproductive organs, especially the develop- 
ment of the eggs. However, certain species will be found to infest 
regularly certain species of mammals, those infesting cattle, rabbits, 
squirrels, etc., each adhering as a rule to its particular species of host. 
Some of these reach a considerable size, as the dog tick, one-half inch 
or so in length, when fully extended with eggs. 
The Acaride are very minute mites which produce itch, scab, 
mange, etc., some of them living on the surface of the skin and others 
burrowing within it. 
LIFE HISTORIES OF PARASITES IN GENERAL. 
In their general life history,many of the parasitic insects travel 
nearly identical courses, owing to the similarity of the conditions 
under which they live. But when we consider the semiparasitic forms 
and free species we meet a great variety of habit. 
The mosquitoes, horse-flies, and buffalo-gnats are troublesome to ani- 
mals only in the adult stage, their early stages, except in the case of 
the flesh-flies living in wounds, or of the bots, being passed in an entirely 
different manner. The mosquitoes, as is well known, live in water as 
‘‘wigglers,” then become pup, still aquatic, then issue in the full-winged 
form, in which stage they make their attacks upon the higher animals 
and finally deposit their eggs on the surface of water. The horse-flies 
pursue a very Similar round of life, but require a much longer time for 
the various stages of development. 
The bot-flies, on the contrary, as already hinted, do all their injurious 
work, except that resulting from fright, in the larval form, at this time 
being parasitic within the host animal. The pupe and adults are 
incapable of harm in themselves. It must be stated, however, that 
the adults are a serious annoyance on account of the terror which they 
inspire in horses, sheep, and cattle when hovering about them to deposit 
their eggs. Whether this terror is due to an instinctive knowledge on 
the part of the animal as to the injurious nature of the insects, as has 
been argued by some, or whether because of their resemblance to bees 
or wasps, or horse-flies, which experience has taught to be capable of 
causing pain, we can not pretend to say with assurance. Certainly, the 
effect of such fright is anything but desirable, except as it serves to 
protect, in some degree, the terrified beast. 
