LIFE HISTORY OF CARPENTER ANT. 203 



covered with a red glass plate, such as described in experiment I., 

 and the other with clear glass. The nest was now exposed to 

 the arc light. At the beginning, the ants were all placed under 

 the red glass, and after the light was turned on, the glass plates 

 were changed about. The ants showed some uneasiness, and yet 

 remained under the clear glass for two hours, seeming to be 

 utterly ignorant of the fact that they were exposed to bright 

 light. As a check on this experiment a similar number of 

 workers from the same colony were placed in a similar nest, but 

 their eyes were not painted. By changing the glass plates I was 

 able to cause them to move from one room to the other fifteen 

 times in thirty-five minutes. This makes it evident that the effects 

 observed are due to the light as perceived through the eyes. 



Experiment V. 



Twenty workers and five queens of C. pennsylvanicus were 

 placed in a hollow cylinder formed by rolling up a strip of fine 

 wire screen and stopping the ends with corks. A centigrade 

 thermometer was thrust through a hole in one of the corks so 

 that the bulb was in the center of the cylinder. The cylinder 

 was now held for an hour about four inches from the arc light. 

 In this position the thermometer registered about 40 C. The 

 ants were exceedingly active all the time, and showed no ill 

 effects afterwards. I have found by other experiments that these 

 ants are able to endure a temperature of 40 ° C. indefinitely without 

 serious effects, but that they are very suddenly killed when the 

 temperature reaches 46 C. 



These results indicate that these ants are adapted to withstand 

 very intense light which is rich in ultraviolet rays, and so, evi- 

 dently, their nocturnal habits are not a result of necessity, but of 

 simple preference. 



There are always some of the workers busy during the day- 

 time of the active season, but the vast majority remain quietly in 

 the nest, and then, a few minutes after sunset, the whole colony 

 seems to awake and the night's labors begin. 



August 12, 1906, I observed the outdoor colony A. I began 

 counting the ants which left the temporary nest at the base of 

 the aphid tree to collect food from the aphids, just as the sun 



