The ants divide labour according to age, with the oldest individuals being trap builders
This ingenious feat of engineering has only ever been observed in one other species of related ant, French researchers say.
The ants cut hairs to clear a path under the plant stem, while leaving some hairs standing to form "pillars" on top of which the lethal platform will sit.
Using the plant hairs they have harvested, the ants weave the platform itself, which is bound together and strengthened using a special fungus.
When the ants have completed the chamber they puncture holes all along its surface, each just big enough to poke their heads through.
Then, hundreds of worker ants climb into the chamber and wait for an unfortunate victim.
"Workers will hide inside the platform, with their mandibles just inside the hole and they will wait there for prey to come," co-author Jerome Orivel of the University of Toulouse, France said.
Anything with legs slim enough to fit through the carefully constructed holes will meet a miserable fate if they are foolish enough to enter the trap.
There is no limit to the ants' ambition - they will try to catch any mammoth of the insect world
Once the prey is well secured by jaws fastening all its extremities, it is stretched over the platform like an ancient sacrifice to the gods.
Scores of worker ants then stream out from inside the trap and sting it vigorously to cause paralysis.
Once the creature is dead or fully immobilised, the ants will carry it to their nest, where they will dismember their prey before carrying it inside.
"Small insects will be immediately dismembered and transported to the nest," said Dr Orivel. "But bigger insects will stay on the trap for up to 12 hours."
There is no limit to the ants' ambition and they will attempt to catch any mammoth of the insect world - so long as it has slender legs.
"Their success depends on the type of insect," Dr Orivel told the BBC News website. "The insects' legs have to be smaller than the holes otherwise they cannot get hold of them.
"The ants must have something to catch - for example, caterpillars will have nothing to get hold of so they will not be preyed upon."
It's not a torture rack. Just a mean snare...