156 The Naturalist in La Plata. 
made : later in the season the old cocoons are 
utilized for storing honey. The wax is chocolate- 
coloured, and almost the only difference I can find 
in the economy of the two species is that the black 
bee uses a large quantity of wax in plastering the 
interior of its nest. The egg-cell of the yellow bee 
always contains from twelve to sixteen eggs ; that 
of the black bee from ten to fourteen ; and the eggs 
of this species are the largest though the bee is 
smallest. At the entrance on the edge of the 
mound one bee is usually stationed, and, when 
approached, it hums a shrill challenge, and throws 
itself into a menacing attitude. The sting is ex- 
ceedingly painful. 
One summer I was so fortunate as to discover 
two nests of the two kinds within twelve yards of 
each other, and I resolved to watch them very 
carefully, in order to see whether the two species 
ever came into collision, as sometimes happens with 
ants of different species living close together. 
Several times I saw a yellow bee leave its own nest 
and hover round or settle on the neighbouring one, 
upon which the sentinel black bee would attack and 
drive it off. One day, while watching, I was de- 
lighted to see a yellow bee actually enter its neigh- 
bour’s nest, the sentinel being off duty. In about 
five minutes’ time it came out again and flew away 
unmolested. I concluded from this that humble- 
bees, like their relations of the hive, occasionally 
plunder each other’s sweets. On another occasion 
I found a black bee dead at the entrance of the 
yellow bees’ nest ; doubtless this individual had 
been caught in the act of stealing honey, and, after 
