112 
ANIMAL INTELLIGENCE. 
III. Black workers, guards, and purveyors ; surround the 
nest as guards or sentinels, in a manner presently 
to be described, and also forage for the food required 
for I. They are much larger and stronger insects 
than either I. or II., and are provided with very 
formidable mandibles. 
The nest is placed in sandy soil in the neighbourhood 
of shrubs and flowers, is a perfect square, and occupies 
about four or five square feet of ground, the surface of 
which is kept almost unbroken. But the boundaries of 
the nest are rendered conspicuous by the guard of black 
workers (III.), which continuously parade round three of 
its sides in a close double line of defence, moving in 
opposite directions. In the accompanying diagram this 
sentry path is represented by the thick black lines. These 
always face the same points of the compass, and the 
direction in which the sentries march is one column from 
south-west to south-east, and the other column from south- 
east to south-west — each column, however, moving in 
regular order round three sides of a square. The southern 
side of the encampment is left unguarded ; but if any 
enemy approaches on this or any other side, a number of 
the guards leave their stations, and sally forth to face the 
foe — raising themselves on their hind tarsi on meeting the 
enemy, and moving their large mandibles in defiance. 
Spiders, wasps, beetles, and other insects, if they venture 
too near the nest, are torn to pieces by the guard in a 
most merciless manner, and the dead body of the van- 
quished is speedily removed from the neighbourhood of the 
nest — the guard then marching back to resume their 
places in the line of defence, their object in desti eying 
other insects being the defence of their encampment, and 
not the obtaining of food. 
The object of leaving the southern side of the square 
encampment open is as follows. While some of the black 
workers are engaged on duty as guard, another and larger 
division are engaged on duty as purveyors. These enter 
and leave the quadrangle by its open or southern side 
along the dotted line marked a to the central point c 
The incoming line is composed of individuals each bearing 
