484 OTHER BLOOD-SUCKING FLIES 



flies if it does not eliminate them entirely. In such cases care 

 should be taken that there Are no small trickling streams which 

 are not readily reached by fish. In the author's experience 

 streams which harbor large numbers of caddis worms, dragon-fly 

 larvae and other carnivorous aquatic insects do not breed black- 

 flies to any extent. 



A considerable degree of protection from blackflies can be 

 obtained by the use of repellents such as are used for mosquitoes, 

 but their efficiency seems to be lost more quickly than in the case 

 of mosquitoes. Moreover the crawling habits of the flies must 

 be taken into account, and other parts of the body than those 

 which are directly exposed must be treated. Blackflies may be 

 driven from houses by fumigation with pyrethrum powder or by 

 any other fumigation method. In camp life the use of smudges 

 is indispensable. An efficient smudge which will last all night 

 can be made in an old bucket with a few holes punched near the 

 bottom. A small fire is started in this and then the bucket is 

 filled with partly wet, punky, decayed wood which will smoulder 

 slowly and produce a dense yeUow smoke. Sleeping in the 

 presence of such a smoke is at first almost as unpleasant as are 

 attacks by mosquitoes and blackflies (the latter becoming active 

 only toward dawn) but one soon becomes accustomed to it, 

 and it has none of the terrible after-effects of an attack by the 

 flies. 



Gadflies (Tabanidae) 



General Account. — Although primarily of importance as 

 blood-thirsty pests of domestic animals, the gadflies or horseflies 

 (Tabanidae) cannot be ignored as biters of human beings, es- 

 pecially as they have been shown to be implicated in the spread 

 of certain human diseases. The bites are painful, and sometimes 

 cause annoyance for several hours; not infrequently these bites, 

 which may bleed, subsequently become infected and give rise 

 to troublesome sores. The females alone are bloodsuckers, the 

 males living chiefly on plant juices. These, flies, of which over 

 2500 species have been recorded, occur in every part of the world, 

 and in every sort of habitat where water or damp places are avail- 

 able for breeding purposes. 



The gadflies are of large size and heavy build (Fig. 224 A). 

 They are often beautifully colored in black, brown and orange 



