66 
Psyche 
[June 
considerable variation, with a wide discontinuity between 
the largest worker and the queen. All of the very small 
workers were found in the nest. Casual observations of 
foraging bees in this area and elsewhere at lower and 
middle altitudes in Mexico where this species is common 
indicate that the smallest workers do not visit the flowers, 
suggesting that a division of labor among workers has 
progressed farther than that described by Brian (1952) 
for B, agrorum (Fabricius). She found that while most 
workers of agrorum eventually forage, small ones begin 
later in life and that a few of the small ones never do so. 
Collections of foraging bees made elsewhere in Mexico 
during July contained a number of queens of B. medius. 
They were visiting flowers just as do queens of temperate 
climate bumblebees in the spring. This observation, to- 
gether with the presence of only a single queen in the 
large nest excavated, throws doubt on von Ihering’s (1903) 
theory that in a Brazilian bumblebee which is either the 
same as medius or a closely allied species colony multiplica- 
tion is by swarms. Perhaps the several fecundated queens 
reported by von Ihering to occur in single nests were most- 
ly young queens which had mated in or temporarily re- 
turned to their parental nests. 
The colony excavated by us would appear to consist of 
the progeny of a single queen. It was just renewing activity 
after a season of reproductive inactivity, probably cor- 
related with the dry season. In spite of its large size, this 
colony probably had not yet passed through the phase 
when new queens and males are produced, for no queen 
cocoons were found in the nest. The disparity in size be- 
tween the queen and workers and the large number of 
queens ordinarily produced in Bombus nests make it un- 
likely that queen cocoons were present, but unrecognized. 
In Brazil, von Ihering (1903) observed fecundated queens 
and some males overwintering in the parental nest. Col- 
lections of B. medius queens visiting flowers in July sug- 
gest that the fecundated queens may pass the season of 
adversity (dry season combined with the cool season) in 
the same manner in Mexico. 
