8 4 
Psyche 
[June-September 
tropical warm temperate distribution throughout the Americas, from 
southeastern and southwestern U. S. to central Argentina and Chile. 
The species are quite closely related and are similar in their habits. 
All form populous nests, at maturity containing 25,000 to more than 
200,000 active and aggressive adult workers. The workers in a 
mature nest vary considerably in size from large soldiers down to 
much more numerous minor workers only 2-3 mm, long, and usually 
only a single functional queen is present. Nest foundation follows 
the pattern typical for ants, in which virgin winged females mate 
with males during a nuptial flight, then quickly shed their wings and, 
as young queens, burrow into the soil and begin the rearing of the 
first brood in a small chamber. Later, as the nest grows, it usually 
comes to be capped by an earthen mound sometimes two feet or more 
high and often two or three feet in diameter. 
Up to the First World War, only three of the fire ant species were 
known to occur in the U. S., of which two, Solenopsis xyloni and S. 
geminata (native fire ant) were found in the southeastern states. It 
seems possible that the “native” fire ant is itself a post-Columbian 
introduction, and it has been spread widely over the tropics of both 
hemispheres by human commerce. In past years, S. geminata had 
gathered to itself much the same reputation as a nuisance now gen- 
erally assigned to the late-coming imported fire ant ( S . saevissuna) 
that is the subject of this discussion. The imported fire ant arrived 
at Mobile, Alabama in produce or ballast at or a few years after the 
end of the First World War. At first the ant (then represented 
solely, so it seems, by a blackish phase with a dull orange band at the 
base of its gaster SB- the so-called “variety richteri ” common in 
Argentina and Uruguay) spread only very slowly in Mobile and its 
environs. At some time around the beginning of the 1930’s, a smaller, 
light reddish form of saevissuna appeared in the Mobile area. This 
phase corresponds to populations of the species common in southern 
Brazil and Paraguay, and it seems most likely that its appearance 
marks a second introduction of saevissuna into the Mobile Bay port 
area. 
Coincident with the advent of the red phase, the entire saevissuna 
salient in southern Alabama entered upon a period of rapid expansion 
that carried the main infestation across state lines by 1940. The 
expansion apparently has not yet reached its full extent, although 
infestations are or have been known to occur in ten states ranging 
from Texas and Arkansas to North Carolina and Florida. Expansion 
occurs in two main ways — by steady widening of the main infested 
areas due to short-range aerial spread of winged females, and through 
