OBSERVATIONS ON BUMBLEBEES. 69 



VI. THE DEFENSE OF THE NEST. 



Wagner (1907) claims that one, or a small number of bumble- 

 bees, even if they belong to a populous colony, never attack, and 

 that the courage of a bumblebee depends upon the number of 

 individuals present. This certainly is not true of species like 

 Bremus fervidus, impatiens, lapidarius, and terrestris. On more 

 than one occasion I have been attacked with great ferocity by 

 single workers of these species at the old nest-site, while the 

 remaining members of the colony were miles away. Equally 

 incorrect, as Hoffer (1888, pp. 97-98), Sladen (1912, pp, 254, 277), 

 and I (1922 a, p. 34) have shown, is Wagner's claim (pp. 144-145) 

 that the members of a bumblebee colony do not cooperate in 

 expelling strange bumblebees from their nest. 



As can easily be demonstrated, the temper of a bumblebee 

 colony depends upon a number of factors. If, for instance, the 

 colony is chilled, even savage species, e.g. Bremus fervidus, 

 exhibit little or no fighting spirit. This lack of temper becomes 

 still more marked if, in addition, the colony has been compelled to 

 fast. The ferocity of a bumblebee colony, to a certain extent, 

 also depends upon previous experience. If the nest of a savage 

 species, like Bremus fervidus, is frequently disturbed, certain 

 members of the colony will attack any one whom they find in the 

 vicinity of their nest. It is probable, therefore, that Wagner 

 (pp. 151-152), at least in the case of Bremus lapidarius and 

 terrestris, based his conclusions on observations which were made 

 at a time when the mettle of his colonies was low as a result of 

 adverse conditions. 



VII. INCUBATION OF THE BROOD. 



There is a difference of opinion among bumblebee students as 

 to why bumblebees incubate their brood. Hoffer (1882/83, I> 

 p. 14) has the following to say concerning this activity: "Die 

 Konigin liegt dabei haufig so iiber der Zelle, dass sie dieselbe mit 

 dem Bauche warmt, wie eine Henne ihre Eier, wobei der Bauch 

 dicht an die Zelle angedriickt wird. Dieses Bebriiten iibt sie 

 iibrigens auch an alteren Eier- und Larvenklumpen und den 

 Puppentonnchen aus." A similar view is held by Sladen (1912, 



to the editor, I took two flourishing bumblebee colonies one of Bremus fervidus 

 and the other of Bremus pennsylvanicus which had their nests within a foot of 

 each other. 



