337 



ORDER DIPTERA. 



(dis, two; and pterorif a wing) 



This order includes many very serious pests, 

 though there are some useful types found in it. 

 The adults resemble somewhat the hymenopterous 

 insects, but can be distinguished from them by 

 having but two wings, while the hymenopterous 

 insects (bees, wasps, etc.) have four. 



Mosquitoes, midges (mosquito-like insects), and 

 flies are included in this order, and some authori- 

 ties include fleas, while others place them in a 

 separate order called Siphonaptera. 



Characteristics of Order Diptera. 

 The two wings are borne by the metathorax; 

 they are membranous and are usually much veined 

 and naked, though the midges have microscoi)ic 

 hairs and mosquitoes have modified hairs in the 

 form of tiny scales which are attached to the veins 

 of the wings. (Plate 41, Fig. 8.) These are very 

 tiny, and do not make the wings opaque, as in the 

 wings of moths and butterflies. In place of the 

 liind wings there is a pair of knobbed processci^ 

 called halteres or balancers. (Plate 40, Fig. 9, Plate 

 41, Fig. 3 a) Their use is not fully understood, but 

 it has been suggested that they act as balancing 

 organs, or as ''rudders" to steer the insect in flight. 

 They are attached to the metathorax. At the base 

 of the wing is a lobe called an alula (Plate 40, 



