The chaco leafcutter ant Atta vollenweideri forms the largest colonies of any social animal on earth.  Mature nests such as the mound pictured here may contain several million ants.  Note the cleared foraging trail leading away from the nest in the foreground.

Resistencia, Chaco, Argentina
The chaco leafcutter ant Atta vollenweideri forms the largest colonies of any social animal on earth.  Mature nests such as the mound pictured here may contain several million ants.

Resistencia, Chaco, Argentina
Leafcutter ants make characteristic circular cuts. Here an ant completes the curve. (Atta cephalotes)

Captive colony at the University of Texas
A busy highway of Atta cephalotes leafcutter ants carrying their bounty back to the nest.

Gamboa, Panama
A media worker of Atta cephalotes finishes off a cut.

Captive colony at the University of Texas
Atta cephalotes in the fungus garden.  Here, the fungus is visible as a white mold growing across the cut leaves that the ants have fed to it.

Captive colony at the California Academy of Sciences
Atta cephalotes. A small worker atop a leaf guards her sister against attacks by parasitic flies.  Ants laden with cargo cannot use their mandibles for defense, so they carry hitchhikers to ward off the parasites.

Gamboa, Panama
Atta cephalotes. Ants carrying leaves are vulnerable to attack by parasitic phorid flies.  To help prevent attacks, small guard workers often ride atop the cut vegetation, mandibles open in defensive posture.  Intriguingly, hitchhiking is only seen in regions inhabited by the flies. Outside the geographic range of the parasites, leafcutter ants do not show this leaf-riding behavior.

Gamboa, Panama
Atta cephalotes, close-up of the head of a soldier.  The sharp mandibles of this ant can easily slice through skin, so handle these ants with care!

Captive colony at the California Academy of Sciences
Atta cephalotes in the fungus garden. Here, the fungus is visible as a white mold growing across the cut leaves that the ants have fed to it.

Captive colony at the California Academy of Sciences
Atta cephalotes in the fungus garden.  Here, the fungus is visible as a white mold growing across the cut leaves that the ants have fed to it.

Captive colony at the California Academy of Sciences
Atta cephalotes in the fungus garden. Here, the fungus is visible as a white mold growing across the cut leaves that the ants have fed to it.

Captive colony at the California Academy of Sciences
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all images and text © Alex Wild 2001-2013