180 Psyche [August 



A UNIQUE METHOD OF DEFENSE .OF BREMUS 

 {BOM BUS) FERVIDUS FABRICIUS.i 



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.' In this case the fate of the intruder may be shown by 

 describing briefly the behavior of a fair-sized colony of Brcmus 

 impatiens Cresson when a queen of Psithyrus lahoriosus 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. 



Dm-ing the summer of 1921, the writer had under observation 

 13 colonies of bumblebees belonging to the following species: 

 Bremus affinis Cresson, Bremus himaculatus 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 lahoriosus 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 



'Contribuiions from the Entomological Laboratory of che Bussey Institution, Harvard 

 University. No. 206. 



2A genus of bumblebees whose members arc social parasites on various species of the 

 genus Bremus, the industrious branch of i.he bumblebee family (Firemidae). 



