Wasps, Bees, and Ants 
5 l 9 
of the black and yellow markings (PL XII, Figs. 5 and 10). A common eastern 
species is B. jerviotus (the “ boiling bumblebee” is good 1 .), which has the body 
of the workers almost all yellow above, only a narrow median band across 
the thorax and the tip of the abdomen being black; B. affinis has (workers) 
the base of the abdomen, its posterior half, and a median band across the 
thorax black, the rest yellow; B. 
terricola has the anterior half of the 
thorax, a band across the posterior 
third of the abdomen, and another 
one on the next to the last segment 
yellow, the rest black; B. calijor- 
nicus , the most abundant species in 
California, has the anterior half of 
thorax and a single narrow band 
near tip of abdomen yellow; B. 
edwardsii, another species common 
on the Pacific coast, has a median 
band across the thorax and a broad 
anterior one across the abdomen and 
the very tip of the abdomen black, 
the rest yellow. 
The strange case of the guest 
bumblebee, species of the genus 
Psithyrus (PL XII, Fig. 4), is almost 
sure to come to the attention of any 
observer of bumblebee-nests. In all 
general characters and total seeming 
truly bumblebee-like, found always 
in and about bumblebee-nests, these 
insidious guests, cleverly living at the 
bountiful table of their host, present 
to us an interesting problem touching 
their deceptively Bombus-like make¬ 
up. Are they really bumblebees, that is, bees directly descended from 
bumblebee stock, which have become degenerate and adopted a parasitic 
life, or are they bees of another stock, which, for the sake of successfully 
deceiving the bumblebees and thus gaining access to their nests, have 
gradually acquired (through long selection) the bumblebee dress and gen¬ 
eral appearance? The former supposition is the more probable. They 
are like bumblebees in so many structural details unnecessary for such 
deception that they must be looked on as a degenerate offshoot from the 
Bombidae. Having given up the gathering and carrying of pollen, their tarsi 
Fig. 724. —Nest of bumblebee, Bombus sp., 
showing opening at surface of ground and 
brood-cells in cavity underneath. (Adapted 
from McCook.) 
