HABITS. 19 



resembling each other; several others equally striking 

 might have been associated in the same group. 



The habits of flies are very diverse. Many are prop- 

 erly spoken of as flower flies — that is, insects whose sub- 

 sistence, for the most part or entirely, is obtained from 

 the honey or pollen of flowers, and the sweetened sap 

 of plants. Among these are many which are swift in 

 flight, spending most of their time during sunny hours 

 upon the wing or resting lightly upon leaves and flowers ; 

 they all love the warmest sunshine. Some mature flies 

 feed upon ordure or decaying material of whatever nature 

 it may be. Many others, including whole families like 

 the Asilidse, Dolichopodidae and Empididae, find their 

 subsistence in the juices of other insects, and are often 

 predaceous in the highest degree. Others, like the female 

 mosquitoes, blackflies and horseflies, are bloodsucking 

 in habit, though not exclusively so, and are often very 

 annoying to man and other warm-blooded animals. The 

 whole group of Pupipara, with the exception of the Brau- 

 lidae, are of this kind, living parasitically upon and suck- 

 ing the blood from mammals and birds. In the previous 

 edition of this work I expressed the opinion that, upon 

 the whole, the order of diptera is beneficial to man's econ- 

 omy, since so many of its members, whether in the larval 

 or adult conditions, are either useful scavengers, destroy- 

 ing that which otherwise might cause distress, or prey 

 upon other and injurious insects. Since the publication 

 of that edition, however, the many marvelous and import- 

 ant discoveries of the parasitic habits of certain very 

 small protozoans which find their intermediary hosts in 

 certain flies, by whose instrumentality they are trans- 

 mitted to man and some of his most valued domestic ani- 

 mals, will require the complete reversal of that opinion. 

 Yellow fever, malaria, and filariasis, transmitted in the 

 saliva of mosquitoes, and the fatal 'sleeping sickness' 



