CHAPTER XI 

 DIPTERA 



79. General Characteristics. The flies (Diptera), consti- 

 tute one of the six major orders. They have two wings, and 

 sucking mouth-parts and they develop indirectly. The larvae 

 of most flies are called maggots. Flies have, in the place 

 of hind wings, a pair of more or less conspicuous knobbed 

 threads or balancers called halteres. Different common 

 names are applied to many flies and groups of flies. Mos- 

 quitoes, gnats, midges, etc., are among these names. 

 Many groups of flies have mouth-parts capable of piercing 

 or "biting" the skin of animals. Mosquitoes and horse- 

 flies are notable examples. Many other forms can eat 

 only exposed liquid food, the sucking tube ending in soft 

 flaps. Few adult flies attack vegetation but many feed 

 on the nectar of flowers. 



80. Importance to Man. Flies are important to man 

 in a rather different way than most other insect pests. 

 While many species attack growing crops and various food 

 products, usually in the larval stage, their greatest im- 

 portance comes from the fact that they attack man and 

 domestic animals directly in the adult stage. In this way 

 they cause not only great annoyance and economic loss, 

 by rendering certain regions p actically uninhabitable for 

 civilized people, but even greater loss by carrying the 

 organisms, which cause certain diseases. Some are parasitic 

 on domestic animals and inflict much injury in this way. 

 The discovery of the disease-carrying powers of many species 



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