204 INJURIOUS AND USEFUL INSECTS 



in a common web, like the larv^ of the lackey-moth ; the 

 larvae of H. euonymella are similar in mode of life, but yellow 

 in colour. 



DIPTEEA 



Structural peculiarities. — The head of a Dipterous fly is 

 very mobile, and much of its surface is usually occupied by 



the large compound eyes. The 

 antennae vary much in structure, 

 as will be seen from the descrip- 

 tions of the chief subdivisions 

 of the order. The mouth-parts 

 are often elongated and con- 

 verted into piercing styles, while 

 the labium encloses the styles 

 and acts as a sucking-tube. 

 The tip of the labium often 

 divides into two lobes {labellce), 

 which may be roughened by 

 raised lines, and serve to tri- 

 turate pollen or other food-sub- 

 stances. There is often a pro- 

 boscis, which may be jointed 

 and retractile. 



The functional wings always 

 form a single membranous pair, 

 except when wings are wanting 

 altogether, which is the case 

 with a very few Diptera. The 

 hind wings are reduced to 

 halteres or poisers, and in 

 Fig. I02.— Mouth - parts of gad-fly that form are a very constant 



{Tahanus). Z^r, labrum ; t?;*, epipharynx ; r *. '-nu r J r it. 



yi/«, m.indibie| Mx, maxilla; Mxp, feature. The function of the 

 maxiiL-iry palp ; z.«, labium ;/>», palette poiscrs is obscurc ; they are of 



of two labellse. ^ , '-',., 



very complex structure, mobile, 

 and in many Diptera can be thrown into rapid vibration ; 

 they are richly supplied with nerves. 



Life-Mstory. — Diptera undergo a complete transformation, 

 with resting stage. The larva never possesses jointed legs, 



