116 GENERAL ZOOLOGY 



The most important family is the Chrysomelidce which 

 contains most of the common beetle pests the potato- 

 bug, elm-leaf beetle, cucumber-beetle, etc. 



Suborder 6. Trimera. This order contains only one 

 important family, the CoccinellidoB y or lady-bird beetles. 

 These little insects both as larvae and adults, do great 

 good to man by feeding on aphids and scale-insects. 



Suborder 7. Heteromera. The darkling and blister- 

 beetles are of considerable economic importance. The 

 former (Tenebrionidce) include Tenebrio molitor, the larva 

 of which is the " meal- worm" so common about flour and 

 grain bins. One of the blister-beetles (Meloidce) when 

 dried and pulverized, has the peculiar property of raising 

 blisters on the human skin, and is used by physicians for 

 that purpose. 



Suborder 8. Rhynchophora. The snout-beetles differ 

 from all others in having the head prolonged into a beak, 

 with tiny mouth parts at its tip. The bark-beetles (Sco- 

 lytidce) are most injurious of all insects to forest trees, 

 causing $100,000,000 worth of damage annually in the 

 United States. The larvae make tunnels beneath the bark 

 of living or dead trees and thus open the way for rot- and 

 decay-fungi. The curculios and weevils damage fruits 

 and grains. 



Order 19. Hymenoptera (Fig. 57). To this order belong 

 the gall-flies, ichneumon-flies, horn-tails, saw-flies, wasps, 

 bees, and ants. These insects possess four membranous 

 wings with few veins; their mouth parts are fitted for both 

 biting and sucking; the female often has a long ovipositor 

 so modified as to form a sting; the metamorphosis is 

 complete. Many of these are of unusual importance to 

 man. There are about 7500 species in North America. 

 Only the most important families can be mentioned. 



The saw-flies (Tenthredinidce) are so named on account 

 of the saw-like ovipositor possessed by the females. The 

 adults are rather inconspicuous, but many of the larvae 

 are well known as rose-, currant-, pear-, larch-, and willow- 



