196 



DIl'TERA OK TKUE FLIES. 



Diptera there is also much variation : some have sucking mouths 

 {Bombylius), others piercing mouths {Tabanus or the Gad-fly), fig. 

 101 ; in the Warble-flies (OEstridce) the mouth is rudimentary, 

 the adults taking no nourishment. There is never a sting ; flies 

 can wound by piercing with the mouth, but not, as is often 

 supposed, by stinging. The labium of the mouth (fig. 101, li) 

 is greatly elongated, and forms a kind of gutter for the reception 

 of the lancet-shaped maxillse and mandibles. The proboscis, 

 made up of the labium, &c., ends in a fleshy swoUen tongue, 

 and is closed above by the labrum. There are no true labial 

 palpi. The head is large, and united to the thorax by a very 

 short neck. The thorax is large and compact, the prothorax 

 closely united to the mesothorax, and forming a thin coUar. The 

 eggs of flies are usually oval or spindle-shaped bodies, of a white 

 or black colour, sometimes laid singly, at others in groups. The 

 larvEe are mostly white footless maggots ; no true legs are ever 



present. Thirteen segments 

 is the usual nimiber present, 

 but in some fourteen may 

 be found (fig. 93, a). The 

 head may be horny or may 

 be reduced .to a simple pair 

 of hooks, the mandibles 

 (fig. 107, d); the body 

 may be naked (fig. 93, a) 

 or with bristles (fig. 109). 

 Most are terrestrial, but 

 some are aquatic — Cvlicidoe 

 (Gnats), Qhironomidm (Midges) (fig. 92), and Eristalidm (Eat- 

 tailed Flies). The genera Volucdla, Tachina, and Conops are 

 parasitic on other insects ; the genera CEstrm and Sarcophagus, 

 &c., on vertebrates. When mature, dipterous larvae may or 

 may not cast off the larval skin. The naked pupse (fig. 97) 

 are veiy varied, often armed with spines and bristles (fig. 99, 5). 

 Those that retain the larval skin as a case are called "puparia," 



Fig. 92. — Plumed Gnat (Clmrontymis pJumosMs.) 



