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Atta cephalotes versus Nomamyrmex esenbeckii

This excerpt is from the research article by Monica Swartz entitled "Predation on an Atta cephalotes colony by an army ant, Nomamyrmex esenbeckii" in the journal Biotropica 30(4):682-684. The locale of the event was in the Corcovado National Park in Costa Rica.

On January 20 1994 at 0901 h, I encountered an Atta cephalotes colony under Attack by Nomamyrmex esenbeckii. The Nomamyrmex were coming down a large cleared Atta trail. Within minutes, the number of arriving Nomamyrmex increased to become a river of ants 8-10 individuals across with additional ants clustered on the trailsides...any Atta on the trail were encased by Attackers.

The Atta colony was small, with surface features that included a main central mound with 4 entry holes and two smaller side mounds with five more holes. Thousands of Nomamyrmex were entering three holes on the main mound with some entry at a side mound. Initially, there was no visible reaction by the Atta. However, within a minute, >100 Atta majors emerged from the central hole, and 20-30 Atta majors emerged from all the other Nomamyrmex entrance holes. Many grasped dry cut-leaf fragments from around the hole entrances, and successfully plugged some holes from within by pulling the leaf fragments over the tunnel entrances. Others used the leaf fragments as a barricade. Holding the leaves vertically, they formed a ring-shaped barrier wall of leaves around the main entrance, and later two other holes. Pushing forward, circa 300 leaf-wielding Atta majors at the main hole expanded the defensive ring barricade to a maximum diameter of 20 cm by 0912 h. By 0910 h, Atta defences were sufficient to prevent any further mound entrances by Nomamyrmex.

Attacking Nomamyrmex still covered the mound. each Atta major, isolated or pulled out of the barricades, was encased by 3-15 Nomamyrmex. These clumps of embattled ants and leaves often tumbled off the mound, continuing to struggle at the mound base.

Meanwhile, the trail of incoming Nomamyrmex became less concentrated...some Nomamyrmex were returning up the trail...until 0923 h when the barricades were breached. With the breakdown of defences at the entrance holes, the Nomamyrmex circumvented the remaining leaf defences and poured into the nest entrances once more.

Immediately, a resurgence of activity ensued on the entering trail. The trailsides again became lined with stationary ants as the trail width increased to five ants across......

Activity around the entrance holes was varied and confused...some holes remained blocked fromw within by leaf fragments. At breached holes, many Nomamyrmex were hesitating to enter. Their reticense increased over the next ten minutes as they waited by the entrances, waving their antennae.

The conflict appeared to be continuing under the surface with no more Atta majors emerging, and the entrance of the Nomamyrmex seemed impeded. However, any internal defences were overcome by 0953 h when the Nomamyrmex suddenly began entering the mound at two entrances in columns seven ants wide and stacked four ants deep....I estimated the entry rate on each hole at ten ants per second and limited only by hole size, with a mass entry of circa 1800 Nomamyrmex per minute.

At 0959 h the first Nomamyrmex came out of the Atta mound with a 3mm larva. By 1033 h, one in ten ants leaving the colony had an Atta larva or pupa.

After the battle, several thousand ants of both species lay dead at the base of the mound. The majority were of the major caste, the largest workers in their respective colonies. In pairs or small clusters, many Nomamyrmex and Atta died with their jaws locked together. The next morning, the remains of dead combatants littered the mound.


Relative to other army ants, Nomamyrmex are robustly built with short, thick appendages, likely an adaptation to fighting large, well-defended ants like Atta. Nevertheless, because the extent of death and damage to the Nomamyrmex appeared considerable, the nutritional rewards contained in an Atta nest must be very high to offset the losses incurred.....

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