INSECTS AND HUMAN WELFARE — DUNCAN 345 



we buy in the markets, we strive to prevent the growth of the several 

 rot-disease fungi that destroy the foundation timbers of our homes 

 and other buildings ; we abhor the maggots that swarm through the 

 carcass of a dead animal or a mass of garbage that has not been prop- 

 erly disposed of; but at the same time we recognize the general use- 

 fulness of decay. We know that decay is the necessary counterpart 

 to life and without decay life would soon become impossible on the 

 earth. 



Folsom and Wardle (5) say that insects "as scavengers are of 

 inestimable benefit, consuming as they do in incalculable quantity all 

 kinds of dead and decaying animal and vegetable matter. This func- 

 tion of insects is most noticeable in the tropics, where the ants, in 

 particular, eradicate tons of decomposing matter that man lazily 

 neglects." 



The importance of decay and the necessity for it lies in the fact 

 that certain chemical elements, in particular nitrogen, phosphorus, 

 and potassium, obtained from the soil by plants and needed alike by 

 plants and animals, are present in usable form only in relatively small 

 amounts in most soils. The available supply must be returned to 

 the soil on the death of the organisms living on or in the soil if life is 

 to be continued in anything like its normal luxuriance. Without the 

 beneficial agency of the bacteria, fungi, insects, and other organisms 

 of decay but especially these three, developing plant life would gradu- 

 ally but surely tie up in plant tissues almost all of the existing supply 

 of critically needed mineral elements. 



For the purpose at hand it is unnecessary to develop in detail addi- 

 tional aspects of the general topic. Simple mention or very brief 

 treatment of some of these will suffice. All, in one way or another, 

 are fairly well known to entomologists though not to the general 

 public, or at least not sufficiently known. 



The importance of insects as animal foods is apparent when we 

 realize that considerably more than half of the food supply of common 

 land birds, fresh-water fishes, many reptiles, and many small mam- 

 mals consists of insects, and without the insects these animals would 

 be unable to maintain themselves. It is customary to consider such 

 animals as constituting checks on the increase of insects, and no doubt 

 at times and perhaps continuously to a limited extent they do consti- 

 tute such checks, but there is much evidence to indicate that more often 

 the vertebrates in question, and in particular the birds, are merely 

 living off of the surplus of insect life and are not a significant factor 

 in regulating insect abundance. 



The dependence of flowering plants on insects as pollen carriers 

 has received wide attention. It is estimated that about 85 percent of 

 flowering plants require insect pollination in whole or in part. Met- 

 calf and Flint (9) estimate that the annual yield of agricultural crop 



