THE DIPTERA. 



405 



mentary trunk. When in the imago or perfect condition they do 

 not take any nourishment ; but inasmuch as they chase horses, 

 oxen, and sheep, and all kinds of ruminants, and frighten them 

 with their buzzing, they are generally supposed to sting the ani- 

 mals, but really they are incapable of doing anything of the kind. 



The Gad Flies, or Tabani, chase the animals in order to suck 

 their blood, but the bot flies seek them in order to lay their eggs, 

 for their larvae live as parasites upon the domestic animals, and 

 ruminating Mammalia generally. The adult fly lays its eggs on 

 the skin of some particular animal, and in some instances they 

 are licked off the skin and are conveyed into the stomach, where 

 they hatch, and the larvae live by sucking the juices of the 

 animal or the matter which their presence produces. Some 

 larvae are hatched on the surface of the skin, and they then 

 bore into the body underneath, and feed there. The larvae 

 are thick, fleshy bots, without feet, and they are covered with 

 rows of spines and tubercles, by which they move about, and 

 they breathe through spiracles, which open at the end of the 

 body. They moult twice, and just before attaining the pupa 

 state they leave the bodies of the creatures they have lived in, 

 and reach the ground, where they undergo their metamorphoses, 

 the pupa being protected by the dried skin of the larva. The 

 bot fly of the horse buzzes about horses and lays its eggs 

 rapidly, and attaches them with a sticky substance to the hair 

 about those parts of the body which the animal is in the habit 

 of licking. The eggs are hatched, and the horse swallows the 

 larvae and they pass down into the stomach, to which they become 

 fixed by means of their hooked mandibles. After a certain time 

 they are passed out with the excrement and undergo their 

 metamorphoses in cracks under the ground. The bot which 

 affects sheep is an object of great terror to them. It lives in 

 its larval state up the passages which lead from the nose amongst 

 the front bones of the head, and produces much suffering. The 

 larvae of some bots, especially those which attack oxen, deer, 

 and goats, dig themselves under the skin of those animals, and 

 produce little tumours ; and this is well known to some birds, 

 for the starlings may be constantly seen at certain seasons of the 

 year looking out for them on the backs and flanks of deer. * 



