THE DISPLACEMENT OF NATIVE ANT SPECIES BY 
THE INTRODUCED ARGENTINE ANT 
I RID OMYRMEX HU MI LIS MAYR* 
By James M. Erickson 
Department of Entomology and Limnology 
Cornell University, Ithaca, New York 14850 
Introduction 
Many authors have described how Iridomyrmex humilis Mayr has 
become a major pest throughout the world (Brun, 1924; Zimmer- 
man, 1940; Smith, 1947; Morley, 1953; Skaife, 1961; Pasfield, 
1968). Once these ants become established in a locality they will 
not tolerate the existence of any other species of ants, and as the 
populations of each colony build up in density, they emigrate in all 
directions, consolidating as they go and driving other species before 
them. Not only does I. humilis displace native ant species, but it has 
been shown to displace other introduced tramp species. The ant 
Pheidole megacephala F. is apparently a native to Africa and has 
been spread by commerce to almost all of the more humid parts of 
the world. It too is a serious pest and displaces native species. How- 
ever, in 1852, in Funchal, the capital of Madiera, this species was 
itself displaced by I. humilis (Stoll, 1898; Wheeler, 1906). The 
displacement of P. megacephala by I. humilis has also been observed 
in the Hawaiian Islands (Wilson and Taylor, 1967; Fluker and 
Beardsley, 1970) and in Bermuda (Haskins and Haskins, 1965; 
Crowell, 1968). Wilson (1951) reports that a local naturalist in 
Mobile, Alabama observed I. humilis displacing the imported fire 
ant Solenopsis saevissima richteri Forel, and Fluker and Beardsley 
(1970) reported the displacement of S. geminata F. in Hawaii. 
Shapley (1920 a, b) describes an “intermittent war” between I. 
humilis and the native California species which he feels would 
eventually eliminate most of the native ant species. Tulloch (1930) 
and Michener (1942) described the displacement of the California 
harvester ant Pogonomyrmex calif ornicus by /. humilis. 
Methods and Materials 
In the present study, the displacement of three ant species, P. 
calif ornicus Buckley, Pheidole grallipes Wdieeler, and Veromessor 
pergandei Mayr, by /. humilis was observed for a six year period. 
Detailed observations of the displacement of P. calif ornicus were 
* Manuscript received by the editor March 2, 1972 
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