FLIES AND DISEASE 13 



bot-flies, I think tliat \vc may regard the occiirrence of fly larvtu in the 

 body of man as entirely accidental and dismiss the matter as being a 

 subject of academic interest rather than one calling for serious con- 

 sideration. Tliere are, of course, the bot-flies, belonging to three dis- 

 tinct families and they are serious pests. In the tropics one si)ccieR 

 commonly attacks man, but the greatest damage is done to domestic 

 animals. Hides are frequently so greatly riddled with "warble" holes 

 as to be almost valueless. 



The bird and bat parasites, as well as the so-called bee-louse 

 {BrauJa caeca), are probably not serious pests although the sheep tick, 

 belonging to the Hippoboscidaj, is often sufficiently numerous to cause 

 serious damage and some species of Hippohosca bite humans in addition 

 to their attacks on horses, camels, etc. 



In many places the so-called blow-flies cause serious loss to sheep 

 owners by "blowing" the wool. 



I have given just a very brief summary of some of the injury 

 caused by flies to animal life, as it affects human welfare, and a very 

 great deal that is of interest has been omitted. One frequently re- 

 ceives inquiries as to the diseases carried by flies, and these few para- 

 graphs may serve to answer the questions. In the following pages, 

 under the families mentioned, additional information is given, particu- 

 larly concerning diseases carried by flies in North America. If the 

 student desires further information on this important subject he should 

 secure a copy of one of the better books on IMedical Entomology. 



Flies and Crops 



It is impossible to enumerate all the flies attacking field, horti- 

 cultural and garden crops, but mention might be made of the various 

 root maggots, the leaf miners, gall makers, fruit flies, grass stem flies 

 and the Hessian fly. The amount of damage done by the groups of 

 insects mentioned must be enormous but it must be remembered that 

 there can be no actual measure of crop damage from a financial ])oint 

 of view. A large crop invariably means lower prices and a small crop 

 higher prices. It is only when individuals or limited communities 

 suffer serious loss in the volume of their produce that there is any real 

 loss, and then it is of a local nature and not national for the producers 

 of the crop affected. It so happens in such cases that one man's loss 

 proves to be another man's gain. While flies undoubtedly do a great 

 deal of damage to our crops and flowers, they are of less importance 

 in this respect than some of the other orders of insects and the Dipt, 

 are, in actual fact, much more beneficial than injurious. 



