CHAPTER XXV 

 ORDER DIPTERA* 



The Flies 



The winged members of this order have only two wings; these are borne 

 by the mesothorax. The second pair of wings is represented by a pair of 

 knobbed, thread-like organs, the halteres; these are present in nearly all flies, 

 even when the mesothoracic wings are wanting. The mouth-parts are formed 

 for sucking. The metamorphosis is complete. 



To the order Diptera belong all insects that are properly termed flies, 

 and only these. The word fly forms a part of many compound names of 

 insects of other orders, as butterfly, mayfly, and chalcis-fly; but when 

 used alone, it is correctly applied only to dipterous insects. To some flies 

 other common names have been applied as mosquito, gnat, and midge. 

 The presence of a single pair of wings and of a pair of halteres is 

 sufficient to distinguish most members of this order from those of all 

 other orders, except in the case of male coccids. 



The wings of flies are thin, membranous, and usually either naked or 



clothed with microscopic hairs; but 

 with mosquitoes the wings bear scales, 

 and with the moth-like flies (Psycho- 

 didse) and some others the clothing of 

 hairs is very conspicuous. The hind 

 wings are represented by a pair of 

 knobbed organs, the halteres; these can 

 be easily seen in a crane-fly (Fig. 488). 

 They are present in nearly all flies, even 

 when the front wings are wanting. 



The mouth-parts of flies are formed 



for sucking, and sometimes also for 



piercing. Their structure differs greatly 



in different families; and in some cases 



fig. 4*88. -A crane-fly, showing wingTand hai- it is exceedingly difficult to determine 



teres - the correspondence of the different parts. 



In the more typical forms the mouth-parts consist of six bristle-like 



or lance-like organs enclosed in a sheath, and a pair of jointed palpi. 



According to the most generally accepted view the six bristles rep- 

 resent the upper lip (labrum), the tongue (hypopharynx) , the two man- 

 dibles, and the two maxillae, and the sheath enclosing these bristles is 

 the lower lip (labium). The palpi which are not enclosed in the sheath 

 are the maxillary palpi. At the tip of the lower lip there is, on each 

 side, a lobe-like appendage; these are the labial palpi. The labial palpi 

 of certain flies are quite large; in the housefly, for example, they are ex- 

 panded into broad plates, which are fitted for a slight rasping function. 

 In their transformations flies pass through a complete metamorphosis. 

 The larvae are commonly called maggots. These are usually cylindrical 

 * Diptera: dis (Sis), two; pteron {wrepbv), a wing. 

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