1941] Nesting habits of Bombus medius 167 
The number of workers in these colonies (and it is presumed 
that all the workers were at home, since the nests were taken 
at night) were 27 in Nest A and 63 in Nest B. 1 
The number of empty cocoons from which workers had 
emerged numbered 39 and 84 respectively. These figures 
are highly interesting from the standpoint of mortality of 
the workers, for we find that the colony with 27 workers had 
actually given birth to 39, and the colony with 63 workers 
had produced 84. The two colonies therefore had lost 12 and 
21 workers respectively. Worker bumblees must brave the 
vicissitudes of enemies and inclement environmnt in their 
foraging expeditions, and one expects a certain portion of 
the population to fare ill, but whether the figures given above 
are much or little one cannot tell, since there is little com- 
parative data at hand. However, in a population study of 
one B . americanorum colony made at the end of the season in 
Missouri, the mortality was much less than in these nests, 
for out of 137 workers born in the colony during the season, 
131 survived until near the end of the season. 2 
The pupae and quiescent larvae within cocoons numbered 
17 in Nest A and 69 in Nest B, and young feeding larvae 
(usually a small number of larvae within a ball-like mass of 
pollen-paste) numbered five (2 in one mass and 3 in the 
other) in Nest A, and three (all in one mass) in Nest B. 
The eggs were placed in small clusters in hollow spaces in 
the interior of the pollen-paste balls. These were without 
openings, and measured roughly about one-quarter inch in 
diameter, and were attached to cocoons and other objects in 
the nest. They were designed to serve as food for the tiny 
larvae when they hatched from the eggs. In Nest A were 
four such masses, containing 8, 7, 6 and 4 eggs respectively. 
In Nest B were two balls, containing 2 and 6 eggs. 
The total potential populations of these nests, including 
queens, workers, larvae and eggs, were 75 and 145. 
As is usual with bumblebees, pollen and nectar are stored 
in vats made of wax-like material ; both are also stored in old 
cocoons from which the bees have emerged. Sometimes 
the cocoons are enlarged for this purpose by placing an 
!13 of Nest B emerged from their cocoons in my jars during the 
following few days. 
2 Entom. News, 52: 70-74, 1941. 
