1922 ] Unique Method of Defense of Bremus fervidus Fabricius 181 
colony No. 7 ( B . fervidus) the proceeding evening, was found 
sitting near the entrance of her nest and, like the Psithyrus 
queen, was completely covered with a sticky liquid. Whenever ; 
this worker attempted to enter the nest, she was immediately 
attacked by her sisters and driven back. The reason for this 
strange behavior and the source of the sticky liquid, which the 
writer at first was unable to account for, were disclosed several 
days later. 
On July 27th a captured Psithyrus laboriosus queen was 
placed in a Bremus fervidus nest and the writer was surprised to 
find that the workers, instead of creating a furore and killing the 
Psithyrus, as do the workers of Bremus impatiens, remained 
calm and resorted to a more peaceful, but equally effective, 
method of expelling the intruder. About a dozen workers 
gathered about the Psithyrus queen, and, after stealthily 
approaching a little closer, each one placed a small drop of 
liquid on the intruder with her mouth. The Psithyrus queen 
did not seem to relish this performance and slowly left the comb, 
apparently seeking to hide herself. A number of workers followed 
her and from time to time added more liquid until she was as 
wet as the Psithyrus queen and Bremus worker referred to above. 
The experiment was repeated with other fervidus colonies and 
was later (September 13th) demonstrated before the Cambridge 
Entomological Club. The members of the club were also shown 
the very different behavior of a Bremus impatiens colony under 
these conditions. 
From July 27th to September 24th a large number of other 
experiments were carried out in order to determine how colonies 
of Bremus fervidus react to other intruders. These experiments 
may be summed up briefly as follows: 
Experiment 1. Introduced: Young queen of Psithyrus 
ashtoni Cresson. 
Result: Daubed with liquid like Psithyrus laboriosus. No 
attempts to sting her. 
Experiments 2, 3 , 4 an( l 5. Introduced (separately) : 
