CHAPTER/ XII 



DIPTERA. ORTHOPTERA, HEMIPTERA AND NEUROPTERA 



THE Diptera, or Two-winged Flies, are a very important group 

 of insects, inasmuch as many of them are the transmitting 

 agents of more or less serious, often fatal, diseases to man and 

 to various domestic animals. They may be defined as insects 

 with a perfect metamorphosis, a sucking mouth, and only two 

 membranous wings, which are naked or more or less hairy, the 

 hind wings being represented by a pair of small knobbed organs 

 called halter es or "balancers." The mouth parts are highly 

 developed, and may be formed for suction or for piercing, while 

 in some the mouth parts are rudimentary in the adult stage. The 

 head is very freely attached to the front of the thorax by a short 

 and usually slender neck, which renders it freely movable. The 

 compound eyes are generally large, often covering nearly the whole 

 upper surface of the head, leaving only a small triangular space 

 on the top for the three simple eyes, or ocelli, which are generally 

 present, and another small space in front for the antennae, which 

 vary considerably in size, form, and structure. The eyes are 

 as a rule larger in the males than in the females, and in the former 

 often meet in the middle line on the head, while in the latter they 

 are separated by a narrow band. The larvag are footless grubs 

 or maggots, generally with a soft body, but sometimes leathery, 

 or even horny. In several species the larvae are hatched within 

 the body of the mother, and in one whole group they are not 

 only hatched but retained and nourished in the egg-passages until 

 they are ready to pass into the pupa state. 



Economically considered, the Diptera may be said to be 

 both useful and harmful insects, for while great numbers act 

 as scavengers, and a few as pollen carriers among the flowers, 

 others ravage various crops, and, as already stated, are the carriers 

 of disease. How truly appalling is their work as disseminators of 

 disease we begin to realise when we come to consider such tropical 



184 



