2 
The flies which cause the above-mentioned troubles belong to two 
families—that of the Estridce , or “Bot Flies” (of which some that 
live in maggot state in swellings, known as Warbles, are thence 
called Warble Flies), and the family of the Tabanidce , or “ Gad Flies.” 
These two families are quite different from each other in their 
habits, life-history, method of injury to stock, and also in some 
important points of their structure. 
The Estridce (Bot, and Warble Flies) are flies of a medium or 
rather large size, that is, for the most part, ranging from about 
three-eighths to five-eighths 'of an inch in length, and often from 
their shape, their hairy or woolly coats, and bright colouring, 
much resembling Humble Bees, and especially distinguishable by 
the mouth parts being small and rudimentary; consequently they 
do not cause pain or injury by biting, or blood-sucking. The 
harm that they do is by means of their larvae, or maggots, passing 
their lives and feeding up to maturity in some part of the infested 
animal. This is usually just beneath the hide, in the subcuticular 
tissues (as in the case of the Ox Warble Fly), or in the stomach 
(as in the case of the Horse Bot Fly), or in the nose or nasal 
cavities (as in the case of the Sheep Nostril Fly); it may occur 
elsewhere, but in this country, and to domesticated animals, the 
above mentioned are the most common localities of infestation. 
Put shortly : in Bot Fly attack, so far as biting is concerned, 
the flies do not hurt the animals; but the maggots do harm by passing 
their lives in feeding somewhere within them, their “hosts.” 
With the Tabanidce, or “ Gad Flies,” the case is quite different. 
These, which are known as “ Breeze Flies,” or “ Horse Flies,” as 
well as “Gad Flies,” vary in size in this country from about a quarter 
of an inch to an inch or more in length, and from three-quarters 
of an inch to one or two inches in spread of the wings. The 
distinguishing point about these flies is that the females are blood¬ 
suckers. The males live on sweet matter of flowers. They are 
furnished with a proboscis, enclosing, in the case of the male four, 
in the female six, somewhat lancet-shaped instruments, which in 
the latter can be driven so effectively into the skin that (as is 
constantly seen) blood flows immediately. 
