CLARENCE HAMILTON KENNEDY. 



temperatures apply to constricta, which is the only species broadly 

 distributed across the central states, while the St. Paul tempera- 

 tures apply to a series of several species such as interim, cana- 

 densis, utnbrosa, etc. Under the Sitka temperatures we find 

 sitkensis, snbarctica and septentrionalis. Such species as palmata 

 and constricta are found in two or three of these zones. 



To define the flying temperatures the mean maximum and 

 mean minimum day temperatures for August have been taken 

 from the Weather Bureau Report for the above stations. 6 Ten 

 degrees was then added to the mean maximum day temperature 

 to give the approximate maximum sun temperature, which is 

 the temperature to which the local dragonflies react positively, 

 while the mean minimum day temperature remained unchanged, 

 as it is a shade temperature to which the local dragonflies react 

 negatively. Thus these temperatures show roughly the range 

 of day temperatures which the species of ^shna meet during 

 their flight season in each of the general zones represented by 

 the temperature records. These records for August are as 

 follows : 



Mean Maximum Mean Minimum 



in the Sun. in the Shade. 



Yuma, Arizona 114 77 



St. Louis, Missouri 96 69 



St. Paul, Minnesota 90 60 



Sitka, Alaska 72 45 



From the above it is obvious that the temperatures during 

 flight do differ greatly for the various species of &shna. How- 

 ever our observations indicate that all lowland /Eshnas are 

 always positive to heat so that the higher the temperature, the 

 greater the activity of the insect. Hine's observations 7 on 

 Kadiak Island w r ere that palmata was most active on the warmest 

 days. Walker's observations 8 on the Canadian species are that 

 increased temperatures always increased the speed of ^Eshnas 

 but his observations do not include temperatures above 90. 

 Somewhere above 90 there may be a limit for this increase of 



6 "Climatology of the United States," Bull. 2, 1906. Temperatures for Yuma, 

 St. Louis and St. Paul. Monthly Weather Review, Dec., 1898, p. 549. Temperature 

 for Sitka. 



7 In conversation with the writer. 



8 Walker, p. 33. "The North American Dragonflies of the Genus jEshna," 

 Univ. of Toronto, Biol. Studies, Biol. Series, No. n. 1912. 



