The True Flies 



The order is not a popular one among entomologists and 

 collectors. Aside from the fact that observations upon their 

 life history are by no means as interesting as some of those which 

 we mentioned in the preceding order, they have none of the 

 beauty which attracts students and collectors to butterflies and 

 moths and they have not the definiteness of structure character- 

 istic of the beetles and they are much more difficult to preserve 

 in collections in perfect condition. The hard-bodied, easily col- 

 lected, and readily pinned beetles seem much more attractive. 

 But the Diptera in many respects possess a peculiar interest and 

 their study is of enormous importance from many points of view. 

 Even in point of beauty, many of the families possess species of 

 striking color and graceful shape; and, everywhere abundant as 

 they are, they are easy objects to collect. It is true that with some 

 of the delicate species, especially the mosquitoes and crane flies, it 

 is almost impossible to preserve specimens in good condition. 

 Still, with many of the groups they keep well when simply 

 killed and pinned and preserve their colors much better than do 

 the dragon flies, for example. 



Very many species, and in fact entire groups, are harmful 

 to man through damage to growing crops and to livestock. 

 One of the most famous crop enemies in the world, the so-called 

 Hessian fly, is a dipterous inject, and most of the insect parasites 

 of livestock belong to this order. As late as 1 884, Dr. S. W. Willis- 

 ton, then of Yale University, an authority upon this order, wrote: 

 " As a whole, the order is a beneficial one to the human economy. 

 While we may resent the troublesome mosquito's and the im- 

 pertinent house-fly's molestations, and while the black fly and 

 the horse-fly may cause the death of many hof'ses and cattle, yet 

 the larger number are purely parasitic in their habits, either in 

 the larval or adult states, upon other and usually injurious in- 

 sects. Many others, too, act as beneficial scavengers of unwhole- 

 some matters, which would otherwise often bring disease and 

 death." Since Williston wrote these lines, a whole class of bane- 

 ful work accomplished by flies has been discovered. That is 

 their agency in the spread of disease. 



As early as 1864, Leidy attributed the spread of gangrene in 

 hospitals during the Civil war to the agency of the house-fly, and 

 the terrible disease known as malignant pustule was afterward 

 discovered to be caused by the bite of one of the gad-flies which 



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