108 ANIMAL LIFE AND SOCIAL GROWTH 



favorable rocky hillsides and hibernate in num- 

 bers in the same locality where the greater heat 

 of the rocks may be a factor in causing them to 

 collect. Lady-bird beetles similarly collect in 

 great numbers in favorable places and may occupy 

 the same location year after year even though, 

 to man, nearby unoccupied niches seem equally 

 desirable. In general, as winter approaches there 

 is a movement into the less exposed niches. In- 

 sects of the upper forest move down to the forest 

 floor and insects and many other animals of the 

 open field or forest margin move into the more 

 protected woodland niches. 



Many of the highly social ants and bees col- 

 lect into dense clusters as winter comes on. The 

 mound-building ants of the Chicago region almost 

 completely desert the upper, exposed parts of 

 their nests and collect in the lower passages just 

 above the water line. Here they gather in 

 great masses that may fill the branching passage 

 in the hard clay so compactly that water cannot 

 enter when the spring thaw raises the general 

 water level of the soil. 



In many cases no apparent benefit results from 

 the collection of the animals in a restricted space 

 in nature. They do benefit by living in the most 

 favorable portion of their available habitat. 

 When these favorable areas are limited in extent, 



