146 TROPICAL MEDICINE AND HYGIENE 



more like a sharp sting, but not producing any subsequent 

 local effects unless infected. Then they may produce 

 a swelling and sometimes an ulcer. They will bite a man 

 or other animal while he is in motion, and seem to bite 

 almost as soon as they alight on him. G. palpalis is often 

 found in boats and canoes, sheltering under the thwarts. 

 Very frequently it will crawl out and bite the legs, and in 

 other cases, as they often fly low, will alight on the legs 

 and bite, whereas the higher flying G. rnorsitans more 

 frequently attacks the upper part of the body, the head or 

 neck. 



They are usually found in narrow belts near water on 

 the edge of forest land, and may in such situations be 

 present in large numbers for a few hours, whilst at other 

 times few or none may be found. They are also found in 

 well-wooded country, in forest clearings, and near forests. 

 The larvae are deposited in the neighbourhood of rotting 

 vegetation, and particularly near the roots of certain 

 plants, such as bananas, as well as many other plants 

 and trees. The pupae are usually found in banks 

 covered with trees near open water, lakes, or streams. 

 Extensive clearings, therefore, form an important part of 

 prophylaxis. 



By the formation of such clearings and the burning 

 off of refuse vegetation in the vicinity of settlements, the 

 actual habitations may be kept clear of these flies. It has 

 been suggested that keeping and breeding fowls, or the 

 importation of jungle fowls from India, might aid in 

 the destruction of such larvae. It is doubtful, however, 

 whether such fowls would have any chance of continued 

 existence at any distance from human habitations, as the 

 larvae also are deposited away from the cleared tracts or 

 in plantations. 



More hope of the destruction of the flies in their adult 

 form may be entertained by the introduction or cultiva- 

 tion of insectivorous insects and other animals, such as 

 dragon-flies. Koch believed that their most important 

 source of food is the crocodile, and advocates the 



