What insects are, and how they are classified 





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Fig. 8. A chewing-louse, or bird-louse. Order Mallophaga 



this is a group of insects in which the adult usually lives only long enough 

 to mate and lay eggs. The nymph, which lives in ponds and streams for 

 perhaps a year or more, eats enough to supply nourishment to last through 

 the short adult life. The nymphs mostly feed on underwater vegetation, 

 and generally have two rows of plate-like tracheal gills (Fig. 23) on the 

 abdomen. 



Mayflies are remarkable in being the only insects to moult again after 

 they have once got their wings. From the aquatic nymph hatches out the 

 first winged form, which is covered with a fine skin, and looks drab and 

 dull; it is called a 'dun' by fishermen, and a subimago by entomologists. 

 Within a day or so this insect moults and becomes a brightly coloured 

 imago, or 'spinner'. 



13. Odonata (North America 425; world 5000) 



Dragonfiies (Fig. 5). These familiar insects are carnivorous as both 

 nymphs and adults, and are fierce enemies of other insects. The adults 

 catch quite big insects on the wing, and the nymphs eat other aquatic 

 insects, tadpoles, and even small fish. - 



There are two main groups: Anisoptera, the 'dragonfiies' proper, are 

 generally bigger and stronger, and have the hind-wings broader than the 

 fore-wings (Fig. 5); Zygoptera, the 'damselflies', are very slender, with 

 both pairs of wings paddle-shaped and alike. 



Dragonfly nymphs (Fig. 24) have the mouthparts specially adapted for 

 feeding on other small animals, including other insects, and can shoot 

 out an organ called the 'mask', and seize their prey. The larvae of 

 Anisoptera breathe by means of short rectal gills, which open internally 

 near the end of the intestine; those of Zygoptera have long caudal gills 

 at the end of the body. 



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