CHAPTER X. 



Arthropoda (continued). 

 Order XVII. DIPTERA (" Two- winged " Insects). 



HERE we have the true flies, which may be distinguished from all other winged 

 insects by one simple fact : the hind-wings have vanished, and in their place 

 are a pair of stalked knobs, known as balancers or halteres. 



The mouth parts are adapted for piercing or sucking. There are two sub- 

 orders. To the first Orthorrhapha belong, amongst others, the gall-midges, 

 fungus midges, the true midges (Chironomidce), and the gnats (Culicidce). 



Sub-order i. ORTHORRHAPHA. 



The adult midges are frequently seen dancing in swarms in the air. Their 

 larvae are generally aquatic. 



The gnats, of which there are at least nine British species, are specially 

 numerous in marshy districts. The Common Gnat (Culex pipiens) is a beauti- 

 ful object under the magnifier, the glossy wings bearing numerous hairs, and the 

 antennae having an exquisite feathery appearance. The female has mandibles. 

 The male is harmless, living on nectar, but the female sucks blood (working 

 by day and night) both from men and beasts, being armed with a remarkable 

 proboscis used for piercing and sucking. The humming sound is produced by 

 the female in flight, and is doubtless intended to attract the male. As many 

 as 300 eggs are laid at a time in water, anchored to a floating leaf or twig. 

 The larvae and pupae may be found in any water-butt. 



Crane-flies or DADDY-LONGLEGS (Tipulidcs) are destructive, as their larvae 

 feed on roots of grass and plants, being known as leather-jackets. The gen- 

 eral appearance of the adult is too well known to need description, but the 

 female has a hard horny " tail " the ovipositor, and may frequently be seen 

 hoveling up and down over grass, in the act of laying her eggs, which are 

 glittering black in colour, and laid in damp places. 



Gadflies (Tabanida) are notorious for the way in which the females suck 

 the blood of horses and cattle ; but the larvae live in damp earth, where they 

 feed on snails, slugs, and beetle larvae. 



Robber-flies (A silidce) prey upon other insects, their larvae living in damp earth. 



The Bee-flies (Bombyliidce) are interesting as illustrations of protective 

 mimicry, for they resemble humble bees in appearance and suck nectar from 

 flowers. The larvae of some species live upon the larvae of the bee. 



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