26 



birds looked over the trees occasionally and still found a few. 

 By the end of another week they had exhausted the supply, and 

 we never have been able to find a single specimen of these 

 psyllas since. Dr. Howard intimates in a bulletin on this 

 insect that the causes which control the increase and decrease 

 in numbers are not fully understood. The birds constitute one 

 agency of control that we can understand. 1 



Professor H. A. Surface reports that Mr. Mann, a well-known 

 pear grower near Rochester, New York, told him that one year 

 the pear tree psylla had destroyed his entire pear crop, amount- 

 ing to thousands of dollars in value, and that in the autumn 

 the eggs of the insects were so numerous that there seemed to 

 be no prospect of a crop the following year, but during the 

 winter white-breasted and red-breasted nuthatches worked in 



flocks in this orchard, with the 

 result that in the spring Mr. 

 Mann could hardly find an 

 insect. Professor Surface asserts 

 that these birds saved Mr. Mann 

 thousands of dollars in that one 

 winter. 2 



One morning in the autumn 

 of 1904 I saw in some poplar 



The red-breasted nuthatch; one of the trees near the shore of the MuS- 



species that saved a pear grower thou- ketaquid River, ConCOrd, MaS- 

 sands of dollars in one winter by 



destroying eggs of the pear tree SachusettS, a flock of myrtle 



warblers and black-poll warblers 



attacking a swarm of plant lice. The insects appeared in 

 myriads; there were so many that it was impossible for me to 

 estimate their numbers. They were mainly in the perfect 

 form, and some of them were in flight. The birds pursued these 

 through the air, but also sought those that remained on the 

 trunks and branches. I watched the operations of these birds 

 at intervals all day. Toward night some of the insects had 

 scattered to neighboring trees, and a few of the birds were pur- 

 suing them there; but most of the latter remained all day 

 about the place where the swarm was first seen. Hour after 



1 Useful Birds and their Protection, Massachusetts State Board of Agriculture, 1907, pp. 153, 154. 



2 Surface, H. A.: Zodlogical Quarterly Bulletin, Division of Zoology, Pennsylvania Depart- 

 ment of Agriculture, Vol. 1, No. 3, November 15, 1903, p. 31. 



