758 NEW YORK STATE MUSEUM 



species, because we are thereby able to ascertain to some extent 

 the limiting agencies controlling them, and the more that is 

 known along these lines concerning various forms, the more 

 accurate will be our judgment as to their possible range. The 

 present year has been marked by the presence in abundance of 

 several interesting species, three of which are mentioned below. 

 The reason for their occurrence in great numbers is probably 

 found in unusually favoring weather conditions, particularly in 

 the more than normal warmth. A study of the monthly mean 

 temperatures during the growing season in the Hudson river 

 valley for this and the preceding four years bears out this con- 

 clusion somewhat. The following tables, compiled from the 

 records of the New York state weather bureau and from those 

 of the New York section of the national weather bureau, show 

 this fairly well. 



Monthly mean temperature of the Hudson valley region 



May June July August September 



1897 59 64.3 73,0. GS.6 61 



1898 57.3 GS.S 73.7 71.8 05.9 



1899 59.7 70.3 72.1 70. S 61 



1900 58.1 69.2 74.1 73.3 66.1 



1901 57.6 69.1 74.7 71.4 63.2 



June Jn 1899, 1900 and 1901 was markedly warmer than in 

 1897 and 1898 and July in both 1900 and 1901 was warmer than 

 the same month in 1897, 1898 and 1899, and this higher temper- 

 ature is more marked in August 1900, which is just about the 

 time of year when many insects would respond most readily to 

 the influence of heat, specially those in the caterpillar stage, 

 and the more than normal warmth would tend to produce 

 greater vigor than usual in this latitude and a consequent 

 increase in numbers the present year. The increased warmth 

 of the last two years is still better shown in the table of monthly 

 means of Albany, compiled from the same sources as the pre- 

 ceding table. 



Monthly mean temperature of Albany 



May June July August September 



1897 59 65 75 70 63 



1898 58.2 69.8 75 73 66.6 



1899 60 71 73.2 72.3 61.4 



1900 57.9 70.5 74.6 74.7 67.7 



1901 59.1 70.2 75.8 72.8 65 



