344 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



suppression of slower-growing trees; and at times insects and disease 

 may serve a useful purpose in removing trees from overcrowded stands, 

 thereby releasing the space to the surviving trees which will then grow 

 more rapidly and into better wood material." 



It is obvious, therefore, that without the beneficial services of numer- 

 ous forest insects our forests would never have attained to their present 

 magnificence, their productivity would be far less than it now is, lum- 

 ber would be inferior, they would be less suitable as homes for valuable 

 wildlife, and their esthetic and recreational values would be far less 

 than they now are. They would, moreover, be filled with a tangled 

 maze of dead branches and small trees that would constitute a fire 

 hazard far greater than any now known, or what is more probable, 

 they would be swept by destructive fires of such extent and with such 

 frequency as never to attain the status of forest maturity as we now 

 know it. 



To consider another phase of the general problem, many insects in- 

 habit the soil, often in tremendous numbers. In one case in Illinois 

 their numbers were estimated at no less than 65 millions per acre. 

 Some of the soil insects, namely wireworms, white grubs, certain 

 aphids and mealybugs, and a miscellany of others, feed on the under- 

 ground parts of plants, damaging them more or less, and at times 

 attain the status of pests. The majority, on the other hand, make a 

 definite, important, and perhaps essential, contribution to the develop- 

 ment of the soil itself and to the maintenance of soil fertility. 



Paul Knight (7) in this connection says — 



(1) Soil organisms cause a continual interchange of soil particles by bringing 

 to the surface particles of subsoil. The gradual enrichment of these soil 

 particles increases the thickness of the rich top layer. (2) The burrows of soil 

 organisms allow better drainage and aeration. (3) The dead bodies of animals 

 such as insects and worms add a large amount of organic material to the earth, 

 (4) The excreta of insects compares favorably in fertilizing value with the di- 

 gestive wastes of other animals. Though the digestive waste of one insect is 

 infinitesimal, the aggregate mass of all insect excreta probably exceeds that of 

 the larger animals and is an important factor in soil fertility. 



W. M. Wheeler (10), referring specifically to the soil-building ac- 

 tivities of ants saj^s, "Thus the ants act on the soil like the earthworms, 

 and this action is by no means inconsiderable, although as yet no one 

 has studied it in detail." 



In the discussion of both of the preceding two topics — forest insects 

 and soil-inhabiting insects — mention has been made of the effectiveness 

 of insects as scavengers. Their value in this connection can more 

 easily be underestimated than overestimated for they are second in 

 importance only to the bacteria and fungi as agents of decay. 



We deplore decay whenever it affects any type of material or prod- 

 uct that we wish to preserve for a time. We deplore the existence of 

 Penicillimn fungi that destroy a part of the oranges or lemons that 



