374 



SOME REPRESENTATIVE INSECTS 



in adults. Wings membranous, posterior pair smaller and rarely- 

 absent. Direct development in water. Species 300. 



Order 7, Odonata. — The dragon-flies and the damsel-flies. 

 Mouth parts mandibulate. Wings four, membranous, and mi- 

 nutely reticulate. Direct development in water. Species 2000. 



Order 8, Thysanoptera (Physopoda). — This includes the insects 

 known as thrips and related forms. Mouth parts suctorial. Wings 



Fig. 192. — The periodic cicada, Tibicen septendecim, one of the Order 



Hemiptera. 



The eggs are laid under the bark of twigs which are slit by the ovipositor of the female. 

 After about six weeks the larvae hatch, and drop to the ground into which they burrow. 

 For seventeen years they live underground, feeding upon decaying material and juicea 

 from roots. Growth is very slow, and the larviE probably molt only four to six times. 

 They come to the surface of the ground, and crawl up on trees where the last molt occurs 

 after the longest larval period known among insects. 



Left: a and b, the adult; c, the molted skin of the last larval stage as it appears after 

 the winged adult has emerged. Right: galleries made by larvae when they come to the 

 surface; a, front view with opening, e; and 6, section showing larvse, at c and d, within. 

 (Left, from Circular No. 132, U. S. Bur. Entomology; right, from Bull. No. 71, U. S. Bur. 

 Entomology.) 



present, rudimentary, even absent in some species. Develop- 

 ment direct. Species 150. 



Order 9, Hemiptera. — These are the true " bugs," such as the 

 eabbage-bug (Fig. 194) , the cicadas (Fig. 192) , the aphids or plant 

 lice (Fig. 200), the scale-insects (Fig. 306, p. 551), and water boat- 

 men. Mouth parts suctorial. Wings usually present. Develop- 

 ment direct with few exceptions. Species 18,000. 



Order 10, Neuroptera. — The ant-lion, the dobson-fly or hell- 

 grammite, and related forms are included in this order. Mouth 

 parts mandibulate. Wings almost always four, completely 

 reticulate. Development indirect, that is, with metamorphosis 

 during a pupal stage. Species 600. 



