What insects are^ and how they are classified 



The snakeflies are more active, and get their name from the long neck and 

 small head. The larvae of both are voracious, those of the alderflies living 

 in water, and having tracheal gills along each side of the abdomen (cf. 

 Fig. 23). Snakefly larvae live under bark. 



23. Mecoptera (North America yoj world 350) 



Scorpionfiies (Fig. 31) are rather like a crane-fly, but with a stouter 

 body and shorter legs. They are recognised by the long, beak-like face 

 and by the upturned tip of the abdomen in the males of one family 

 (Panorpidae), from which they get the name scorpionfly. 



The larvae of Mecoptera are like caterpillars, and the Order is related, 

 on the one hand, to the butterflies and moths, and on the other to the 

 true flies. 



24. Trichoptera (North America 950; world 4500) 



Caddisflies (Fig. 32). Adult caddisflies are rather like moths, but have 

 the wings covered with hairs instead of scales. They can be found on 

 water-side vegetation, and sometimes far away from water, especially at 

 night when the adults are commonly attracted to lights. The larvae live 

 under water, and most of them make themselves a 'case' from small stones 

 and other debris, sticking it together with silk. The larvae carry their cases 

 about when they move: they may be either herbivorous or carnivorous, 

 and some carnivorous larvae construct a net of silk to catch other insects 

 in the flowing water. 



25. Lepidoptera (North America 10,500; world 200,000) 



Butterflies and moths (Figs. 15, 34, 35, 37, 39-41). Everyone knows what 

 these look like. The wings are covered with scales, arranged in a pattern 

 that is often very beautiful, and Lepidoptera have always been favourite 

 insects with collectors. 



For most purposes the popular division into butterflies and moths is 

 accurate enough, though a few groups do not quite agree. Butterflies are 

 day-flying insects, with large wings and a small body, the antennae have 

 a small knob at the tip, and the two wings of each side are not locked 

 together. Moths are mostly night-flying (though a few appear in daylight), 

 with a fatter body and smaller wings, the antennae have no knob, though 

 they may be peculiarly shaped, and the two wings of one side are generally 

 locked together, either by a projection backwards from the fore-wing 

 (jugum) or a bristle projecting forwards from the hind-wing (frenulum). 



Another popular way of dividing the Lepidoptera is into Macrolepi- 

 doptera and Microlepidoptera, or 'macros' and 'micros'. This is mainly 

 a grouping by size, but by general agreement some of the biggest moths 

 go into the ' micros ', because they are obviously related to the others in 

 that section. Modern scientific classification is based on the arrangement 

 of the veins of the wing, and on the structure of the genitalia (Chapter III), 

 and on details of the life-history, especially of the pupal stage. 



Sometimes Lepidoptera are wingless in the female sex, though the 



19 



