282 METAZOAN PHYLA 



isms. They may injure man by affecting in similar ways his domestic 

 animals. Insects may destroy grain, fruit, and vegetable crops or 

 ravage forests, and they are the cause of serious damage to a great 

 variety of manufactured products. The annual losses due to insect 

 pests in the United States have been estimated in recent years at close to 

 $1,000,000,000. 



316. Benefits from Insects. — To offset these injuries some benefits 

 are to be credited to insects. Perhaps the most prominent benefit is 

 the destruction of injurious insects by certain others which thus become 

 beneficial. Some insects themselves are made use of by man, examples 

 being blister beetles, used in medicine, and the cochineal insect, which 

 is a source of coloring matter. The products of insect work, such as 

 the silk of the silkworm and the honey and wax of bees, may also be 

 utilized. A few insects are used by uncivilized races as food. A very 

 curious use of ants by the Indians in South America, described by Bruner, 

 is in a sort of surgical procedure where they serve in place of sutures in 

 holding the margins of wounds together. The ants used are large and 

 have powerful jaws. Bringing the margins of the wound together with 

 one hand, the "surgeon" holds the ant with the other and permits it to 

 bite through the two margins. When the jaws are locked, the body is 

 torn from the head and the locked jaws remain in position until healing 

 has closed the wound. Then they are removed. In this country and 

 in Purope, fly maggots have recently been made use of in surgery. 

 Introduced into wounds in which there is a considerable amount of dead 

 and decaying tissue, they remove this, thus paving the way for the 

 filling in of the wounds by regenerating healthy tissue. 



One relation of insects, which is important in the preservation of the 

 normal checks and balances which regulate all animal life, is that they 

 form a very large part of the food of other animals, particularly birds. 

 Their abundance under normal conditions provides an adequate food 

 supply for such animals, many of which themselves are of great value. 

 Some of these economic relationships will appear in the discussions which 

 follow. 



317. Injurious Types. — Some of the more common and familiar of the 

 injurious insect types may be briefly reviewed. The food of the termites 

 (Fig. 181) consists of dead wood; they sometimes attack piled lumber, and 

 in the tropics they are a scourge because of their attacks on dwellings, 

 furniture, and all other articles made of wood. In the Eastern states their 

 ravages, however, are chiefly observed in the tunneling of dead logs in 

 forests. Termites shun the light except when a new brood of winged 

 individuals swarms, mating occurs, and new colonies are established. If 

 lumber is removed from contact with the ground and placed upon cement 

 blocks or stones, making it necessary for the termites to come to the light 

 to reach it, the wood will not be attacked, as it wouJd be if placed upon 



