444 PROCEEDINGS OF THE AMERICAN ACADEMY. 



was now placed around the nest to keep out the light, the lamp being 

 left in the same position, but the screen having been removed. After 

 five minutes the thermometer reading was 25° C, and the ants were 

 in commotion.- I then poured cold water over the outside of the nest 

 till the ants became fairly quiet, the thermomoter standing at 22.5° C. 

 When the thermometer had reached 20° C, the lamp was again placed 

 near the nest, and at the first intimation of motion among the ants a 

 reading of the thermometer was taken; it showed 21° C. But pre- 

 viously, when there was light and no rise of temperature the ants were 

 quiet at 22+° C. The nest was now cooled to 19° C. and the ants 

 began to move at 20° C. It therefore seems fair to assume that the 

 stimulus is not simply heat, but a rise of temperature. To see the 

 effect of light other than red, at the same power, a 16-C. P. incandes- 

 cent lamp with an ordinary glass bulb was now used, at the same dis- 

 tance that the ruby light had previously been, with the water screen 

 in place. At the end of two minutes the ants were disturbed, but they 

 seemed to be less disturbed by the light of a 16-C. P. incandescent 

 lamp than by its heat. From these two experiments it seems clear 

 that we are dealing here with the stimulus of heat from the ruby bulb 

 rather than of light. Heat is really a natural stimulus to ants, as 

 they are in the habit of coming up under stones or to other warm parts 

 of the nest, and of taking there the eggs, larvae and pupae to warm 

 them. Moreover, in the Barth nest I found that so long as the heat 

 was not too intense, the ants took their young toward it ; if, however, 

 it became very intense, from placing the lamp nearer the nest, they 

 carried them away. So long as the behavior of the ants indicated 

 that the warmth was favorable to them, so long, I think, we may safely 

 say that it was a natural stimulus. 



C. Out-door Work. 



That I might study ants under entirely normal conditions, I worked 

 during the spring, summer, and autumn of 1909 on out-door colonies of 

 Cainponotus herculeanus pictus a.t Randolph, N. H., and oi Phcidole pili- 

 fera at Cambridge, Mass. In order to obtain as natural results as possi- 

 ble, the observations were made in many cases without touching the 

 nest at all, and in no case was there any disturbance of the ant when it 

 could be avoided. To this end, before making observations, I often 

 waited for a time after seating myself on the ground so that the ants 

 might recover from any stimulus to activity caused by my approach. 

 In making notes or in preserving ants, all individuals sharing in any 

 activity under the influence of any excitement, other than that which 



