THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 53 
be tunneled into the ground. The depth will depend upon how far 
it is necessary to go to find the needed amount of moisture. It is in 
the underground nest also that the most comfortable temperature 
can be found, both in summer when it is very hot and in winter 
when it is very cold. In the cities the walls of buildings often are 
utilized, the ants taking advantage of the artificial warmth and 
shelter afforded. In rainy weather, when the soil is very damp, the 
underground nest will be abandoned for a location above ground, 
in buildings, trees, piles of dry weeds, piles of lumber, etc., and 
under almost any kind of shelter. When the ants are caught in the 
ground by a sudden rain, in situations where there are no convenient 
trees, buildings, or other shelter, " sheds " are constructed out of 
particles of soil and trash along the surface of the ground. These 
sheds are sometimes very large and are elaborately tunneled into 
galleries and pavilions. They dry out much more rapidly than the 
packed soil of the ground, and the young are kept in them until the 
ground again becomes dry. 
OFFSHOOT NESTS AND RUNWAYS. 
The ants habitually construct temporary quarters and utilize nat- 
ural shelters along the foraging trail, especially if the food supply 
is distant from the nest, as places in which to rest, secluded from 
light, heat, and wind, and in which wandering queens may hide. 
If the food supply is large, attracting many ants for a long period, 
the ants gradually construct runways, or series of shelters, between 
the nest and the food source, tunneling them in the ground or build- 
ing them up of particles of soil and trash, according to circum- 
stances. As these structures are built toward the sources of food 
and the queens are more or less constantly traveling in the trails of 
the foragers, it is in this direction that the colony expands. When- 
ever one of these wandering queens finds a suitably dark and secluded 
spot along the trail she makes her abode there permanently, de- 
posits eggs, and starts a secondary colony. Queens, eggs, and young- 
occur almost constantly in the larger, more secluded shelters along 
the foraging trails. This is the most important means of local 
spread of the colony. 
A good illustration of the formation of offshoot nests in the ground 
occurred in the field poisoning tests at New Orleans. A supply of 
poisoned sirup kept near a fig tree for several months in 1913 
attracted ants from three colonies in turn, all of which finally de- 
serted the neighborhood. On October 2 workers from a fourth 
colony, nesting in an outbuilding 72 feet distant, arrived, and by 
October 8 the file of ants from nest to jar had increased enormously. 
