106 



THE MEXICAN" COTTON-BOLL WEEVIL. 



ature prevailing in the exact spot where the individual weevils are hiber- 

 nating that determines the date of emergence from hibernation. Piles 

 of grass in the open field are warmed by the sun in February and March, 

 and the weevils emerge from them at that time. The shaded places 

 of the forest or swamp are cool and damp, and they do not reach an 



Fig. 22.— Diagram illustrating average length of hibernation period of the boll weevil as related to date 

 of entering hibernation. (Original.) 



equivalent temperature until some weeks afterwards, and the wee- 

 vils consequently emerge later in such places than in the open fields. 

 The bunches of moss are so resistant to heat that even in the hottest 

 days of summer they are very noticeably cooler than the air. 



EMERGENCE FROM HIBERNATION. 



TIME OF EMERGENCE. 



The time of emergence of the boll weevil from hibernation ranges 

 from February 15 to July 1. It is necessary to discuss the conditions 

 which cause tins irregularity. A careful study of all the series of 

 experiments to determine the immediate causes for the first decided 

 impulse to emerge has resulted in the following conclusion : That the 



