INSECT ORDERS 



257 



the larvae bore through to form "warbles" or "wolves" and the adult fly 

 eats its way out when it matures. 



6. Flesh flies. These live in the decaying flesh of dead animals and 

 some of them are called "blow flies" because they live in and around the 

 bodies of bloated animals. Some are called "screw worms" because the 

 female deposits tiny living larvae in open sores of animals such as horses 

 and cows and they work around in the sore. These are sometimes de- 

 posited in the nose of man and work around in the nasal cavity and 



Courtesy Southwestern Biological Supply Co. 



Fig. 17.13. Botfly larvae attached to the stomach of a horse. This stomach has 

 been removed after the death of the horse and the inner lining is shown here with the 



many larvae attached to it. 



sinuses until they pupate and eventually fly out of a nostril a full grown 

 fly. Some species are beneficial ; it has been found that they will eat 

 only dead flesh and are sometimes put in human wounds to clean out the 

 decaying flesh and speed up healing of the healthy tissue. 



7. Tachina flies. Parasites on caterpillars in the larval state. Live 

 larvae are laid on the caterpillar's back by the female tachina fly. These 

 larvae work inside the caterpillar and live on its body. The caterpillar 

 forms a pupa, but a number of dark colored sluggish flies hatch out in- 

 stead of a moth or butterfly. 



8. Tsetse flies. A blood sucking fly that inhabits a large part of 

 Africa and spreads the dread disease of sleeping sickness discussed in 

 detail in Chapter 7. 



