62 THE AKGENTINE ANT. 
An account of the methods used by the Argentine ants in over- 
coming other species of ants was published by the senior author * 
in the Journal of Economic Entomology. 
Prof. W. M. Wheeler, in Entomological News for January, 1906, 
gives an interesting account of the way in which this species obtained 
a foothold in Madeira and supplanted another introduced species, 
Pheidole megacephala Fabr. 
coccim: and aphidiixe. 
The liquid excretions of the various species of scale insects and 
aphides form one of the chief sources of food for the Argentine ant. 
The large variety of trees and plants in the South gives support to a 
great number of coccids and plant lice, and these insects in turn 
yield sustenance to myriads of ants. In return for this food supply 
the ants shelter and protect these insects, with the result that the 
latter increase beyond all customary proportions. As the result of 
this symbiotic manner of living we find that a comparatively small 
area of land frequently supports enormous numbers of ants, scale 
insects, and aphides, while the plants themselves become so severely 
infested that some of them are killed and many more seriously 
injured. 
All through the summer months, and also during warm days in 
winter, heavy streams of ants can be seen ascending and descending 
the trees and plants; the ascending ants empty, the descending ones 
heavily laden with the liquid excretion which they have obtained 
from the various scale insects and plant lice. During the summer 
this activity is well-nigh endless, and the ant trails can be observed 
at all hours of the day and night. All scales and aphides are closely 
attended, but some species appear to attract more of the ants than 
do others. The large unarmored scales and the plant lice appear to 
be the chief favorites, the mealy-bugs, however, following them very 
closely in this regard. 
Aside from protecting the aphides and scale insects from ladybird 
beetles and constructing earthen shelters over them, the ants only 
rarely foster them directly. In one case only have insects of this 
character been actually found in the ants' nests. In January, 1909, 
Mr. G. D. Smith, in excavating an underground colony at Baton 
Rouge, found a number of barnacle scales, Ceroplastes cirripediformis 
Comst., on tree roots which passed through the formicary. These 
scale insects were full grown and vigorous. At this season of the 
year no live scales of this species could be found above ground. It 
may be remarked in passing that this is one of the species to which 
the ants are very attentive during the summer and autumn months. 
1 Notes on the Habits of the Argentine or "New Orleans" Ant, Iridomyrmex humilis Mayr. Wilmon 
Newell, Journ. Econ. Ent., vol. 1, no. 1, pp. 21-34, 1908. 
