Vol. XLVII. August, IQ24. No. 2. 



BIOLOGICAL BULLETIN 



MISCELLANEOUS BIOLOGICAL OBSERVATIONS ON 



BUMBLEBEES. 1 



O. E. PLATH, 

 COLLEGE OF LIBERAL ARTS, BOSTON UNIVERSITY. 



Although the biology of bumblebees has been a favorite study 

 of numerous amateur and professional naturalists, many ques- 

 tions concerning the life-history and habits of these interesting 

 insects are still unsolved. In several recent papers (1922 a, b, c; 

 1923 a, 6), I have discussed some of these questions, and in the 

 following paragraphs wish to touch briefly upon several others 

 which, because of their heterogeneity, could not be incorporated 

 in the earlier papers. 



I. CONDITION OF PILE AND NESTING HABIT. 



In his monograph on the bumblebees of Thuringia, Schmiede- 

 knecht (1878) expresses the belief that loss of thoracic pile in 

 bumblebees indicates that the colonies to which such individuals 

 belong have subterranean nests. That this theory is incorrect 

 is shown by the following observation. On July 6, 1921, I 

 transferred a surface nest of Bremus (Bombiis) fervidus to an 

 observation-box in which the colony was kept until the first part 

 of October. At the time the nest was taken, the pile of all the 

 members of the colony, including that of the queen, was in 

 perfect condition, and remained that way until the latter part 

 of July, when the dorsal side of all the foraging workers became 

 coated with a layer of yellow pollen. These layers of pollen 

 gradually hardened and sometimes reached several millimeters 

 in thickness. The bees evidently were annoyed by these lumps 

 of pollen, for they repeatedly tried to rub them off with their 



front legs. Whenever they succeeded in doing so, most of the 

 pile on the dorsal side of the thorax came off with the pollen, 



1 Contributions from the Entomological Laboratory of the Bussey Institution, 

 Harvard University. No. 226. 



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