Wasps, Bees, and Ants 



5*9 



of the black and yellow markings (PI. XII, Figs. 5 and 10). A common eastern 



species is B. jerviotus (the " boiling bumblebee" is good!), 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 (PI. 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.) 



