540 The Animal Kingdom 



back, forming a heavy wing cover. The second pair is membranous 

 and used for flying. The bodies of most are hard and compact. 

 Mouth parts chewing, size highly variable. Many of great economic 

 importance due to destruction of food plants ; others such as the 

 carpet beetle destroy fabrics. This order contains about 40 per cent 

 of known insects and numbers at least 250,000 species. 



Order 5. Trichoptera (Caddis Flies). Mothlike forms with aquatic 

 larvae and pupae. Chewing mouth parts with reduced parts. Adults 

 with two pairs of membranous wings, long filamentous antennae. 

 Larvae build cases of small stones, sand, or bits of other materials. 

 Important as an article of diet for fish in fresh-water streams and 

 lakes. About 4,450 species. 



Order 6. Lepidoptera (Moths and Butterflies). Adults with two pairs 

 of wings with scales (except for a few forms) ; adult mouth parts 

 usually much reduced, of the siphoning tube type. Many with bril- 

 liantly patterned wings. Economically this order has many im- 

 portant forms whose larvae feed on crop plants, trees, bushes, etc., 

 and on fabrics. The silkworm has long been important as a source 

 of silk. About 112,000 described species. 



Order 7. Dipt era (Flies, Mosquitoes, etc.). Typically the adults have 

 but a single pair of transparent wings ; mouth parts vary in type, 

 body form likewise variable. Economically one of the most impor- 

 tant group due to their transmission of diseases. The parasitic larvae 

 of some (the bots) cause much damage to cattle. The fruit fly 

 (Drosophila sp.) has been one of the most important forms in the 

 study of genetics. There are some 85,000 described species, but 

 undoubtedly many forms are unknown. 



Order 8. Siphonaptera (Fleas). Adults wingless with stout spiny legs 

 and short antennae. Mouth parts are piercing-sucking type. Most 

 species small. Feed on the blood of mammals and birds. The 

 eggs are laid either on the host or simply dropped in the nest. It is 

 very difficult to find the eggs, larvae, or pupae; economically very 

 important as pests of man and his domestic animals. Bubonic 

 plague is transmitted from rats to man by the rat flea. 1,100 species 

 are known, but the number of individuals in a single infection may 

 be tremendous. 



