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. 



