The Displacement of Native Ant Species by the Introduced Argentine Ant Iridomyrmex Humilis Mayr

Many authors have described how Iridomyrnex humilis Mayr has become a major pest throughout the world (Brun, I924; Zimmerman, 94o; Smith, 947; Morley, 953; Skaife, I96.I; Pasfield, 968). 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 o.f the more humid parts of the world. It too, is a serious pest and displaces native species. However, in I852, in FUnchal, the capital o.f Madiera, this species was itself displaced by I. humilis (Stoll, 898; Wheeler, I9O6). The displacement of P. megacephala by I. humilis has also. been observed in the Hawaiian Islands (Wilson and Taylor, I967; Fluker and Beardsley,, 97o) and in Bermuda (Haskins and Haskins, I965 Crowell, 968). Vilson (I95I) reports that a local naturalist in Mobile, Alabama ob.served I. humilis displacing the imported fire ant Solenopsis saevissima richteri Forel, and Fluker and Beardsley (I97o) reported the displacement of S. geminata F. in Hawaii. Shapley (i92o a, b) describes an "intermittent war" between I. humilis and the native California species, which he eels would eventually eliminate, most of the native ant species. Tulloch (I93O) and Michener (i942) described the displacement of the California harvester ant Pogonomyrmex californicus by I. humilis.