This paper is the third of a series of papers dealing with the biology of species of bumblebees found in Illinois. In the first paper (1928), the salient features of the bionomics of Bremus bimaculatus (Cresson) were recorded in a more or less detailed manner and much information presented regarding methods and technique. The second paper (1929) deals with the biology of Bremus impatiens (Cresson). For details regarding how much of the data used in this paper were secured, the reader should consult my two previous papers of this series, particularly the first one of 1928.