32 



highly beneficial from their habit of preying on other insects 

 such as plant lice, scale insects and similar forms. 



Order IX. Diptera. The Two-winged Insects. 



The chief characteristic of this order is the fact that 

 the adults never have more than one pair of wings. The 

 first pair is developed, the second being represented by small 

 structures called halteres or balancers. 



This order includes the true flies. These insects are 

 very numerous, and are diverse in habit, but all agree in 

 the possession of one pair of wings, the complete metamor- 

 phosis and the mouth parts in the adult formed for piercing 

 and sucking, or for lapping. The name of the order is 

 derived from the Greek words dis, two, and>e?'o/, a wing. 



Fig. 29. Diptera. House-fly, 



Puparium at left; adult next; larva and enlarged parts at riqht 

 Enlarged. (From U.S Dept, Agric.) 



Eepresentatives of the order are the house-flv (Fig. 29) 

 the blow fly, mosquitoes (Fig. 30), and sand flies (merry- 

 wings). The larvae are maggots, or, in the case of mosquitoes 

 water wrigglers. They live in a variety of situations 

 according to their manner of life. Some are scavengers, 

 breeding in manure and decaying organic matter ; others 

 attack the leaf, flower, fruit or stem of plants ; while others 

 are direct parasites on man or on the lower animals. Some 

 are distinctly beneficial on account of their habit of preying 

 upon, or of parasitizing, other insects. 



