2SG Annals Entomological Society of America [Vol. X, 



always deposited either outside the observation box, or in a far 

 corner of the nest. When examining the comb in the observation 

 box, I frequently removed all the glass covers, without danger of 

 alarming the inmates or of being attacked by them. Of course, 

 if one were to breathe into, or jar the nest, the workers would 

 be aroused to action. It was evident that this sj^ecies could be 

 bullied by another species of Bombiis, when one morning I dis- 

 covered a worker of B. peunsylvaniciis running about on the 

 comb of this B. auricomiis nest, and helping herself to honey. 

 The auricomiis workers were aware of the presence of this alien 

 bumblebee, but acted as if afraid to attack the invader. On the 

 other hand, when a worker of auricomiis is introduced into a nest 

 of pennsylvanicus it is immediately attacked and killed. 



B. auricomiis is probably victimized by most of the common 

 parasites of bumblebees, but whether any species of Psithyrus 

 infest the nests I am unable to state. One worker, which I found 

 dead on the floor of the nest one morning, contained a full grown 

 larva of Conopida^, Zodion obliquefasciatum Macq. in her abdo- 

 men. Mites of the family GamasidcB were also found in the nests. 



In central Illinois, B. auricomus is not a very common 

 species of bumblebee. 



EXPLANATION OF PLATES. 

 Pl.\te XXI IL 



Fig. 1 . View of ihc nesl of B. auricomus Robt. on June 27, 1916, showing: a, queen; 



b, workers; c, original honey pot. Reduced. 



Fig. 2. View of the nest of B. auricomus Robt. on June 27, 1916, showing: a, queen; 

 leaving the nest; b, worker brooding on egg cells; c, cocoon full of 

 honey, partly capped with wax; d, first empty cocoon, containing 

 pollen; e, empty egg cell. Reduced. 



Plate XXIV. 



Fig. 3. View of the nest of B. auricomus Robt. on June 27, 1916, showing: a, 

 empty cocoon from which first worker emerged; b, original honey-pot; 



c, wax-covered cocoon; d, small brood cells. Natural size. 



Fig. 4. View of the nest of B. auricomus Robt. on July 7, 1916, showing: a, first 

 empty cocoon; b, brood mass, containing medium-sized larvae in 

 separate cells; c, cocoon full of honey, partly capped with wax; d, 

 original honey-pot; e, extra cells added to original honey-pot; /, wax- 

 covered cocoons. Natural size. 



