STATE HORTICULTURAL SOCIKTY. i 2 I 



as numerous as now, and, with that astounding acceleration of increase 

 characteristic of geometrical progression, they would multiply until in 

 about twelve years we should have the entire State carpeted with insects, 

 one to the square inch over our whole territory. I have so arranged this 

 computation as to exclude the insoluble question of the relative values of 

 birds and predaceous or parasitic insects, unless we suppose that birds eat 

 an undue proportion of beneficial species. 



Take another view of this matter. According to the computation 

 of Mr. Walsh, the average damage done by insects in Illinois amounts to 

 twenty millions dollars a year. Large figures certainly ; but when we 

 find that this means only about fifty-six cents an acre we begin to see 

 their probability. Few intelligent farmers or gardeners would refuse an 

 offer to insure complete protection, year after year, against insects of all 

 sorts, for twenty-five cents an acre per annum, and we will, therefore, 

 place the damage at one-half the above amount — ten million dollars per 

 annum. 



Suppose that, as a consequence of this investigation, we are able to 

 take measures which shall result in the increase, by so much as one per 

 cent., of the efficiency of birds as an insect police, the effect would be a 

 diminution of the above injury to the amount of sixty-six thousand dol- 

 lars per annum, equivalent to the addition of over one-and-one-half 

 million dollars to the permanent value of our property; or if, as is in 

 fact a most moderate estimate, we should succeed in increasing the 

 efficiency of birds five per cent, we should thereby add eight-and-one- 

 fourth millions dollars to the permanent wealth of the State, provided, as 

 before, that birds do not eat unduly of beneficial species. 



These figures will be at once rejected by most naturalists as absurdly 

 low. The young robin of Prof Treadwell (a bird whose fame has 

 extended over both hemispheres) required not less than sixty earth-worms 

 a day, equivalent to at least two hundred and fifty average insects, to keep 

 it alive. A pair of European jays have been found. Dr. Brewer informs us, 

 to feed their brood half a million caterpillars in a season, and to eat a 

 million of the eggs in a winter.* 



Compared with these numbers, my seven thousand two hundred 

 insects a year seem certainly many times too few; and similar criticisms 

 might very probably be made on other items of the estimate. I prefer, 

 however, to put these matters with a moderation which will command 

 general assent, especially as we see that the importance of the subject 

 does not require exaggeration. Of course the individual farmer or gar- 

 dener could, by intelligent and careful management, if he knew just what 

 to do, increase the value of his own birds far beyond his individual share 

 of the above-mentioned general aggregate. 



It is thus made probable that the birds intervene continuously between 

 us and the complete destruction of our most important industries — the 



* A young mocking bird {Mimus polyglotlus), raised from the nest by my nephew, 

 Robert Forbes, ate about 240 red-legged grasshoppers daily — equivalent to at least 480 

 average insects. 



