What insects are^ and how they are classified 



29. Coleoptera (North America 27,000; world 280,000) 



Beetles (Frontispiece; Figs. 64-67). Although this is an immensely- 

 successful group, and there are nearly as many different kinds of beetle 

 as of all other insects together, yet most people can tell a beetle at sight. 

 The plates of the body are particularly strong and well-jointed, and the 

 average beetle, alive or dead, is tougher than almost any other insect. 



The fore-wings are hardened into elytra:, or wing-cases, which normally 

 cover the abdomen, and add to the well-armoured appearance. The range 

 of size in beetles is remarkable. The smallest beetles are less than half a 

 millimetre long, and the longest is about 150 mm. — i.e. 300 times as long. 

 The bulky Goliath beetle of the tropics is about 100 mm. long, so that its 

 bulk in comparison with the smallest beetles is 200^: i, or 8 million to one. 



Though most beetles can fly, and frequently do so, at night as well as 

 in the daytime, they are more particularly insects of the ground, and are 

 found most commonly in soil, among debris, under bark, and on vegeta- 

 tion. They have chewing mouthparts, and eat almost every possible kind of 

 solid or semiliquid food; a few even suck blood through grooved mandibles. 



Like the water-bugs (Fig. 19), the water-beetles divide into those that 

 are fully aquatic and those that merely skate on the surface. The Gyrinidae 

 (Whirligig beetles. Fig. 5 id) are the skaters, and live only on animal prey, 

 The deep-water beetles are the fiercely predatory Dytiscidae (Fig. 51b) 

 and the plant-feeding Hydrophilidae, though the larvae of both families 

 are carnivorous. The adults of these water-beetles are fully able to live 

 out of water, and often fly, especially at night. 



Larvae of beetles are most varied in appearance (Fig. 33). Many have 

 thoracic legs, and run actively; others are white, fleshy, and curved into 

 the shape of a letter C, and move little; others still are completely in- 

 active, legless, and with reduced antennae and mouthparts. The form of 

 the larva is suited to its way of life : the active ones, with legs, are generally 

 predatory; the soft, legless larvae live on or in an abundant supply of 

 vegetable material. 



30. Strepsiptera (North America 120; world 300) 

 Twisted-Winged Insects get their common name from the peculiar 



modified club-shaped or paddle-like front wings of the male. They are 

 also sometimes called 'stylopids', after the typical genus Sty lops. They 

 are a degenerate group, whose larvae are parasitic in other insects, 

 especially the Homoptera and Hymenoptera. The adult female never 

 completely emerges from the puparium, but remains partly visible be- 

 tween the abdominal segments of the host. The effect of the parasitism 

 is to cause both structural and physiological distortion in the host, which 

 is then said to be 'stylopised'. The male Strepsipteron has wings, and is 

 free-living. 



The true relationship of these insects is not certain, but they are 

 usually placed close to, or included in, the Coleoptera. Although they are 

 so obscure, 300 species are known. 



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