INTRODUCTION. IX 



Diptera may always be recognized by the presence of but 

 one pair of wings ; the second pair of other insects is really 

 represented by a small organ on each side back of the true 

 wings, consisting of a short, slender stem with a knob-like ter- 

 mination, called the halteres or poisers. Their function is 

 not known ; that they have some function seems certain, as 

 they are always in vibration during flight. Not all flies are 

 winged; in some degraded forms, both among the lowest and 

 highest groups of the order, they may be entirely wanting, as 

 also the halteres. Sometimes the males will have wings and 

 the females be wingless. But the number of wingless forms 

 is very small. 



In the adult state the habits of flies are very various. Some, 

 but not a very large proportion, are predaceous upon other 

 insects, sucking their juices. Some are very annoying to man 

 and other warm-blooded animals, sucking their blood ; of these 

 may be mentioned the mosquitoes, black-flies, horse-flies, sta- 

 ble and horn flies, the tsetze fly, etc., as well as all the pupipara, 

 which are parasitic upon birds and mammals. By far the 

 largest number of diptera, however, feed upon vegetable sub- 

 stances, either fresh or decaying, the pollen and honey of 

 flowers, etc. Some feed upon ordure and decaying material 

 of whatever nature it may be. 



In the larval stages, the habits are yet more diverse. Brief 

 references to the larval habits will be found in the following 

 pages. Suffice here to say that the larger part are vegetable 

 feeders, but not a few live upon decomposing animal matter, 

 or in the living bodies of other insects, snails, reptiles, birds, 

 mammals, etc. While some members of the order may be 

 very annoying or prejudicial to man's economy, the order, 

 upon the whole, is a beneficial one, whether in the larval or 

 mature stages, whether as parasites upon other, and injurious 

 organism, or as scavengers. 



In the following pages I endeavor to give such definitions 

 and descriptions of the mature insect as will enable the stu- 



