80 THE ARGENTINE ANT. 
RESEMBLANCE TO OTHER ANTS. 
There is little difficulty in distinguishing Iridomyrmex Jiumilis 
Mayr from its nearest American relative, Iridomyrmex analis Ern. 
Andre. The latter species is quite common in cotton fields and other 
situations^ in the South, is much lighter in color than Jiumilis, and 
possesses a very disagreeable odor which is entirely lacking in the 
case of Jiumilis. The clearly marked trails of the Argentine workers, 
when on their foraging expeditions or when moving from place to 
place, have no counterpart in the case of analis, the workers of which 
in large measure forage independently of each other. I. analis 
constructs inverted cone-shaped mounds or craters on the surface 
above the underground nests, while what little dirt is excavated by 
Jiumilis is scattered about the entrance to the nest in promiscuous 
fashion, the ants evidently desiring to rid themselves of the exca- 
vated pellets as expeditiously and conveniently as possible. The 
" wet- weather sheds " of the Argentine ant, construe ted. only during 
or just after prolonged rainy spells, bear no resemblance whatever 
to the craters of analis; but on the contrary are more or less flat, 
composed of fine particles of earth, unstable in structure and supported 
by grass or leaves. 
However, the superficial resemblance of I. Jiumilis to several spe- 
cies of other genera is even closer than to I. analis and is sufficient 
to make positive identification of Jiumilis well-nigh impossible ex- 
cept by one skilled in detecting the characters used by myrmecolo- 
gists for classification. Among the southern forms most likely to 
be mistaken for I. Jiumilis, and vice versa, may be mentioned the 
" crazy ant" (Prenolepis longicornis Fab.) and Dorymyrmex pyra- 
micus Roger. The workers of both these species are of practically 
the same size and color as those of Jiumilis and the workers of all three 
travel and forage in much the same way. Prenolepis is distinguished 
from I. Jiumilis by its camponotine characters, particularly the shape 
of the gizzard, by the cloacal orifice being round rather than slit- 
shaped, and by the presence of stiff, erect hairs upon the body. Dory- 
myrmex is easily distinguished by the conical or pointed elevation 
upon the epinotum (last dorsal segment of the thorax), a structure 
that is entirely lacking in Iridomyrmex, the epinotum of which is 
evenly convex. 
The resemblance of I. Jiumilis to still other species is sufficient to 
be confusing at times, but one can, by a process of eliminating certain 
easily observed characteristics, determine with reasonable probability 
whether a colony of living ants belongs to this species or not. First 
to be noticed is the size of the ants under suspicion. The workers of 
the Argentine ant are from 2.2 to 2.6 mm. in length, the largest indi- 
