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Tropical ants build and set a trap that resembles a medieval torture rack. They use this ingenious setup to capture insect prey much larger than themselves, then rip the victim apart.

These ants have transformed the characteristic ant zeal for teamwork into something macabre. Azteca brevis ants build and set a trap not unlike a medieval torture device, which is used to cooperatively capture and rip apart insect prey.

Lead author first came across ants in Costa Rica鈥檚 in 1999. He saw the ants constructing unusual, porous nests on tree trunks. But he could not find any research explaining what these structures were for.

After months of observations and experiments in the rainforest, Schmidt and his colleague of the University of Toulouse in France discovered that A. brevis ants were engaging in an ingenious ambush hunting strategy.

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The millimetres-long ants build a network of galleries and tunnels, reinforced with fungus, in the tree trunk. The end result is a Swiss cheese-like contraption, dotted with holes just wide enough for a worker ant鈥檚 head. Schmidt calls it a 鈥渃arton nest鈥�.

The ants lurk in the holes, jaws agape, waiting for a large grasshopper or leafcutter ant ( spp.) to step onto the trap. When one does, an ant will clamp onto a leg and start pulling. At this point, the victim is doomed.

鈥淏y trying to set itself free, the Atta ant would then step in yet another hole where the same process was repeated, until the legs and antennae of the Atta were all fixed and the intruder was spread-eagled on the carton nest,鈥� says Schmidt.

After pinning the insect down, the A. brevis ants carve it up on the spot. The trap allows workers to efficiently kill insects nearly fifty times heavier than themselves.

A nifty trick

Dejean has also seen an unrelated ant species () in French Guiana . This suggests that the strategy has evolved at least twice, independently.

鈥淸The trap] is quite unique and so far limited to the very specific lifestyle and ecological niche of these two arboreal ants,鈥� says Schmidt.

Farmers in Costa Rica are increasingly using fungicide in the ants鈥� native range. This may imperil the species by killing the fungus used to reinforce the trap tunnels and galleries.