24 



HIBERNATION 



With the approach of cold weather the ants become inactive and 

 gather together in a few of the main galleries of the nest with their 

 larvae, occupying at that time a very limited region compared with 

 the large area occupied by their extensive tunnels in the summer 

 time. I have never found anything but queen, workers, and larv?e 

 in the nests in late fall, winter, or early spring. I have never found 

 males or winged females of this species in winter, although it is quite 

 common to find the winged forms of some other species in the nests 

 during the winter. This shows that the winged forms all leave the 

 nests in the summer or autumn. My observations show that the ants 

 are very little, if any, deeper in the soil in winter than in summer. 

 In fact, they seem to use their largest summer tunnels for their 

 winter quarters. The first few days of January, 1909, were very 

 warm. The frost was out of the ground in the open fields so the 

 farmers could plow. January 4, I followed a plow in an old corn- 

 field, and found in the bottom of the furrows a large number of nests 

 of L. nigcr aiiicricaiiiis exposed, just as one finds them in the spring 

 and summer. The ground was so cold that the ants were quite stupid 

 and very inactive, and they were huddled together in masses with 

 their larvae. Such masses could be picked up in places by handfuls, 

 when the ants would very slowly crawl about over one another. They 

 were far too stiff and inactive, however, to have moved with their 

 large bunches of larvae from the deeper galleries during those few 

 warm days, so they must have been in these same galleries during 

 the previous part of the winter, and would have remained there all 

 the rest of the cold weather. As the ants were warmed by the heat 

 of the hand, or that of the laboratory, they soon became as lively as 

 ever and resumed their normal activities. 



Drouth will drive the ants down intO' the soil much deeper than 

 cold. In very dry weather I have followed their tunnels to a depth 

 of 22 inches, and often in the summer time many of their main 

 galleries are eight to ten inches deep. In the fall of 1909 I marked 

 a number of nests of L. nigcr aiiicricaiius in an old corn-field, and at 

 various times during the following winter examined one or more of 

 them. I found the ants at the depths one finds them during the sum- 

 mer, that is, from just below the surface to eight and ten inches 

 down. Most of the ants and their larvae were from four and a half 

 to seven inches down, although I found some not more than two 

 inches below the surface when the ground was frozen to a depth of 

 five and six inches. When the ground was frozen the walls of the 



