Argentine Ant
Iridomyrmex humilis

Argentine Ant, Iridomyrmex humilisArgentine ants are the eensy teensy, fast moving, black ants that make massive assaults on garbage cans and other sources of sweet or greasy foods.  From South America, they arrived in Louisiana around 1890, in southern California in 1908. Argentine ants wipe out native species, not by being stronger, but simply by overpowering numbers.

Argentine Ant, Iridomyrmex humilisA broad column of ants moving pupae from a flooded nest to a nearby dry one. The nest for Argentine ants is small and shallow, under a walk or a flat slab on the ground, more like a temporary field camp than the capital of a colony.  In fact, it turns out that there is only one colony of Argentine ants in Southern California.  It stretches from the Mexican border to the bay of San Francisco.

Argentine Ant, Iridomyrmex humilisIn this close view of a nest, you can see some of the ants.  There are actually many ants in the picture, moving too fast for the shutter speed of the camera.  The white objects are pupae, often mistaken for eggs.  Sometimes I find this nest occupied and sometimes not.  I also find nests under a board lying on concrete, in piles of dead leaves, inside the motor housing of a kitchen mixer.

Argentine Ant, Iridomyrmex humilisUsually the ants are seen outside (at least at my house) hurrying along two way trails like this one.  The problem is that during rainy winter weather when the ground gets saturated, or during hot, dry summer days, the ants come inside where conditions are more pleasant.  In a matter of minutes myriads of ants can appear in a bathroom (for water) or kitchen.  While you sleep, they can move their nest into any conveniently confined space.

Argentine Ant, Iridomyrmex humilisAny raised, unobstructed path, such as a garden hose, or as here, the top of plastic lawn edging, can be a freeway for the ants.

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