THE DIPTERA 



325 



on living animals, producing an irritating substance. The action of this and the 

 feeding on the tissues cause the animal to become thin, lose its appetite and 

 frequently death follows, for fresh eggs are repeatedly laid in the same wounds 

 by the adults. The larvse mature in 4 or 5 days in living animals and more 

 slowly in dead ones, and, on becoming full-grown, drop to the ground which 

 they burrow into a few inches to pupate. The pupal stage lasts from 3 days to 

 2 weeks and, at the end of this time, the adult flies emerge, completing the life 

 cycle in from 1 to 4 weeks according to the conditions of the weather. 



FIG. 344. Full-grown Screw-worm Maggot, greatly enlarged. 



Bull. 857.) 



(From U. S. D. A. Farm. 



Control. Most of the breeding of these insects is in dead animals and there- 

 fore all carcasses should be promptly buried or burned. To protect living live 

 stock, efforts to prevent their injury must be made and all cases of injury cared 

 for as soon as possible. This may be done by pouring a little chloroform into the 

 wound. It is then generally advisable to remove the maggots and clean the 

 wound with water containing 5 per cent of carbolic acid. Pine tar over the out- 

 side at the wound will act as a repellent to the flies. In serious cases, the services 

 of a veterinarian will be needed. Tick wounds are often the starting points for 

 screw-worm injuries, and ticks should, therefore, be controlled as far as possible. 



The Tsetse Flies (Glossina of several species). These Muscid flies 

 are the conveyers to man of the dreaded disease known as " sleeping 

 sickness." The insects occur only in parts of Africa where they are 

 found along wooded streams and where large game animals are present. 

 The mouth parts of these flies include piercing structures and the insects 

 normally attack the wild game, but man is also liable to their visits. 

 The disease is caused by a Protozoan animal (Trypanosoma gambiense) 

 obtained by the flies while feeding on infected animals, and the trypano- 

 somes may be directly conveyed into another animal during the next 

 day or two, after which the fly becomes innocuous for about 4 weeks: 

 by this time, those of the parasites which entered the stomach of the fly 

 have gone through a development in the body of the insect and have 

 gathered in the salivary glands. The fly is now dangerous for about 3 

 months. In man, the disease appears as an irregular fever, and an en- 

 largement of the glands followed after a time by nervousness and sleep, 

 the patient becoming comatose and finally dying. The earlier stage of 

 the disease may last for several years but the last usually continues only 

 from 4 to 8 months. 



