180 
Psyche 
[August 
A UNIQUE METHOD OF DEFENSE OF BREMUS 
(. BOMBUS ) FERVIDUS FABRICIUSj 
By O. E. Plath, 
Massachusetts Institute of Technology, Cambridge, Mass. 
It is a well-known fact that bumblebees, especially the 
more ferocious species, are quick to attack with sting and 
mandibles if any vertebrate ventures too close to their nests. 
Similar punishment is meted out by many species if their nests 
are invaded by bees which do not belong to the colony, e. g. 
Psithyrus. 2 In this case the fate of the intruder may be shown by 
describing briefly the behavior of a fair-sized colony of Bremus 
impotiens Cresson when a queen of Psithyrus laboriosus Fabricius 
enters, or is placed in, its nest. As soon as the stranger is detected 
on or near the comb, a general uproar arises in the colony. The 
intruder is seized immediately by numerous workers, stung to 
death, and thrown out of the nest. This, in general, seems to be 
the behavior of a large number of Bremus species whose habits 
have been studied. But, as we shall see presently, one of our 
most common New England bumblebees, Bremus fervidus 
Fabricius, behaves very differently under these conditions. 
During the summer of 1921, the writer had under observation 
13 colonies of bumblebees belonging to the following species: 
Bremus affinis Cresson, Bremus bimaculatus Cresson, Bremus 
fervidus Fabricius, Bremus impatiens Cresson, and Bremus 
vagans Smith. Each colony was kept in a glass-covered box 
which was provided with a flight-hole so that the life of the 
colony could go on unhindered. On July 24th, the writer noticed 
a disheveled Psithyrus laboriosus queen crawling out from the 
nest material of colony No. 7 ( B . fervidus ) and removed her to a 
separate box. She was wet all over, her pile being matted against 
the integument by a sticky liquid. On the same day a worker 
of colony No. 8 ( B . im.patiens) which had been placed near 
'Contributions from the Entomological Laboratory of the Bussey Institution, Harvard 
University. No. 206. 
2 A genus of bumblebees whose members are social parasites on various species of the 
genus Bremus, the industrious branch of the bumblebee family (Bremidae). 
