Economic Importance of Animals 565 



beetles are quite destructive of stored grains. The bean weevil (beetle) 

 larva attacks bean and pea seeds, rendering them useless for planting 

 or food purposes. The adult June beetle is a household annoyance in 

 early summer, besides eating plant foliage. The larvae or white grubs 

 do great damage to lawns and underground vegetation. The elm leaf 

 beetle destroys large numbers of elm and other trees. The Colorado 

 potato beetle destroys potato plants and other garden vegetation. This 

 beetle migrated into Colorado from Mexico and has since spread to the 

 East and West. The blister beetles, when dried and pulverized, produce 

 a blister when applied to the human skin. The mealworm beetle is used 

 as food for pet birds. It is quite common in grocery stores, flour mills, 

 and granaries. The leaf-chafing beetles feed on the pollen, flowers, and 

 leaves of plants. The Japanese beetle has been very destructive to 

 plants, especially grasses, since its appearance in New Jersey in 1916 

 and its subsequent spread to other parts of the country. The bark 

 beetles produce a damage of over $100,000,000 annually to forest trees 

 in the United States. Many species of the so-called long-horned beetles 

 are very destructive of shade, fruit, and forest trees. Some of the more 

 common species are the maple tree borer and the apple tree borer. The 

 cotton boll weevil causes millions of dollars' damage to cotton crops in 

 the South. The scavenger beetles are quite beneficial because they bury 

 or eat decaying materials, thus reverting them back to the soil where 

 they can be used by future plants. This cleaning activity also rids the 

 surface of the earth of them where they might be annoying if allowed 

 to accumulate. What would be the condition of the earth if all the 

 animals and plants of the past were still lying on the ground? 



Order 17 — Mecoptera: Both the larvae and adults of the scorpion 

 flies (Fig. 298) are carnivorous and feed on numerous smaller insects. 



Order 18 — Trichoptera: The caddice flies (Fig. 299) are of no great 

 economic importance. The aquatic larvae build characteristic protec- 

 tive cases of small rock, sand, leaves, and grass. The cases of each 

 species are characteristic of that species. How do these supposedly 

 stupid, aquatic larvae know what type of case pattern to build in order 

 to display their characteristic racial coat of arms? 



Order 19 — Lepidoptera: The saliva of the silkworm (Fig. 300) pro- 

 duces the true silk of commerce. The larva of silkworms spins a cocoon 

 of a single, continuous strand over 1,000 feet in length. This thread 

 must be unravelled and woven together with others in order to make a 

 single silk thread. Is it difficult to see what makes true silk cloth 



