Atta cephalotes: Castles of Sand

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Atta cephalotes - Castles of Sand.

Atta cephalotes: Castles of Sand

Photo by Dr. Lisa Reed
Website: Rutgers University

This nest of Atta cephalotes was photographed in the Asa Wright Bird Sanctuary, in Trinidad in 2003.

The nests of mature Atta colonies can attain physically daunting proportions, exceeded only by the gigantic nest mounds of African Macrotermes termites. Young colonies typically have only a few nest mounds, with foraging holes opening several meters away from the mounds, but the numerous (up to hundreds of nest openings) nest mounds of large mature colonies sometimes fuse together to form one huge mound. In this case, the central nest mound may be 30 m in diameter, have numerous 0.3 m diameter feeder mounds extending outwards to a radius of 80 m, and may occupy 30 to 600 square meters! More amazing, the underground chambers may extend downwards to more than 6 meters in depth!

The immense size of Atta nests, and the very large populations of the colony, can cause problems in terms of creating enough ventilation throughout the nest to prevent the high build-up of CO2 and loss of oxygen. There are two mechnisms by which leafcutter ants may prevent from suffocating.

In the first method, called thermal convection, the hundreds of nest openings in mature Atta nests create a ventilation system that continuously circulates air throughout the nest. Because the central chambers tend to have the brood chambers and gardens, these areas become somewhat warmer than the peripheral chambers. The warm air moves up and out through the central hole openings, drawing colder air from the outer chambers into the central area. This in turn draws fresh air from the outside into the nest holes on the periphery.

The second method is called wind-induced ventilation, and this was elucidated by Kleineidam, Ernest, and Roces (2001). In this case, air is drawn out of the central nest mound openings by wind blowing over the nest openings. This outflow in turn causes air to rush into the nest via the outlying nest holes and tunnels, thus ensuring the rapid circulation of air throughout the nest chambers.

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