16 



stomachs of these birds, but only insects; and that he con- 

 cluded that if the birds were killed off all vegetation would be 

 destroyed by insects. 1 Here we have the chief reason why the 

 huge caterpillars of polyphemus, cecropia and luna moths, 

 which are capable of doing immense damage, rarely become 

 numerous enough to be noticeable. When the settlers on our 

 great western plains first began to plant trees to provide wind- 

 breaks on the prairies they introduced the eggs or cocoons of 

 large moths on the young trees. As there were no tree birds 

 then in the region, the larvse of the larger moths, such as 

 polyphemus and cecropia, multiplied exceedingly, making it al- 

 most impossible to grow trees, but as groves and orchards 

 finally became established, and arboreal birds spread over the 

 country, nesting and rearing their young in the trees, these 

 caterpillars were reduced to comparatively harmless numbers. 2 



Dr. Robert T. Morris of New York City wrote me on Decem- 

 ber 7, 1917: 



i 



My own special hobby is the hybridizing of nut trees upon my country 

 place at Stamford, Connecticut. In order to do this work I cover branches 

 carrying pistillate flowers with large paper bags in order to protect the 

 flowers from any pollen except that which I wish to introduce. These 

 bags commonly remain in place two or three weeks. The leaves are not 

 removed from the branches, but are tucked into the paper bags. I found 

 that under the protection of these bags insects increased to such an extent 

 that they sometimes destroyed all the leaves, and almost always destroyed 

 or injured so many of them that the branches which had been covered 

 stood out distinctly from the rest of the tree all summer long. It was 

 necessary for me to resort to the plan of dusting the leaves thickly with 

 Persian insect powder, or spraying them with Pyrox before enclosing them 

 in the bags. 



Of course the bags excluded from the branches so covered not 

 only birds but other natural enemies of insects. Nevertheless, 

 any attempt by man to protect or propagate insects for any 

 purpose soon demonstrates that birds are very potent and per- 

 sistent enemies of those insects. Mr. E. P. Felt, working under 

 my direction, in the year 1891, confined numbers of gypsy 

 moth caterpillars in bags of netting stretched over the limbs of 



1 Samuels, E. A.: Birds of New England, 1870, p. 156. 



2 Useful Birds and their Protection, Massachusetts State Board of Agriculture, 1907, pp. 109, 

 110. 



