436 



THE BOT-FLY. 



the Tabanidse. As with the preceding family, the larvae of the Asili reside under ground, 

 and feed upon the roots of plants. 



The family of the Syrphidae, or Hoverer-flies, is rather large, and contains many inter- 

 esting insects. Among them may be mentioned the Volucella flies, which feed, while in the 

 larval state, on the larvae of bees and wasps, and, as if to aid them in gaining admission into 

 the nests of those formidable creatures, are shaped and colored so like the insects which they 

 invade, that at a little distance it is almost impossible to distinguish between them. 



The DRONE-FLY (Eristalu tenax) belongs to this family. This insect bears a wonderful 

 resemblance to the hive-bee, and has a habit of moving the abdomen in a manner that leads an 

 unaccustomed observer to fancy that it possesses a sting. The larva of this insect is popularly 

 known by the name of Rat-tail maggot, on account of its peculiar construction. This larva 

 resides in mud, with the head downwards. In order to enable it to breathe, the respiratory 

 tubes are carried into a long and telescopic appendage attached to the tail, the end of which is 

 furnished with a brush of hairs something like that on the tail of the gnat larva. The 

 extremity of this curious organ is always held out of the muddy water, and it is most curious 

 to see the grubs elongate their tails as the depth of water is increased. 



All the vast family of Muscidae, or Flies, are members of this order, and as at least eight 

 hundred species of this one family are known, it may be imagined that no description of 

 them can be attempted. 



THE large and bold looking fly, represented in our illustration, belongs to the family of the 

 CEstridae, and is popularly known by the name of BOT-FLY. All these insects are parasitic in 

 or upon animals. The larva of this Bot-fly resides in the interior of horses, and is conveyed 

 there in a very curious manner. The parent fly deposits her eggs upon the hairs near the 

 shoulders of the horse, where the animal is sure to lick them in order to rid itself of the 

 unpleasant feeling caused by agglutinated hairs. The eggs are thus conveyed to the stomach, 

 to the coats of which organ the larvae cling, and there remain until they have attained their 

 full growth. They then loosen their hold, are carried, together with the food, through the 



bed interior of the animal, fall to the 



ground, and immediately begin to 

 burrow. They remain underground 

 until they have undergone their meta- 

 morphoses, and then emerge in the 

 shape of the perfect insect. They do 

 not seem to inflict any damage upofi 

 the animal from whose bodies they 

 have drawn their nourishment, and 

 some veterinary surgeons believe that 

 they are rather beneficial than in- 

 jurious. 



Another kind of Bot-fly ((Estrus 

 boms) resides in the cow, but instead of being taken into the stomach, it burrows into the 

 skin, and there forms large tubercles, that are popularly called worbles or wurbles. An 

 aperture is always left on the top of the tubercle, and the larva breathes by means of 

 keeping the two principal spiracles opposite to the orifice. When full grown, they push 

 themselves out of the aperture, fall upon the ground, and there burrow and undergo their 

 transformations. 



The spiracles, to which allusion has been often made, are the apertures through which air 

 is admitted to the system. Insects breathe in a very remarkable manner, the air being con- 

 ducted through curiously-constructed vessels to every part of the body, even to the extremities 

 of the feet and antennae. It will be seen that the structure of these vessels must be very 

 remarkable, on account of the opposite duties they have to perform. As they penetrate the 

 entire insect, it is needful that they should be flexible, in order to permit the creature to move 

 about at will, as, if they were stiff- walled, the joints would be rendered useless, and the insect 



HORSE BOT-FLY. Gastrophilus eyui. a, Fly. b, Egg on a hair, c, d, e. Larva in 

 its transformations. 



