Actually, this was tested very elegantly by E.O. Wilson, the world's leading ant expert.
When an ant dies, the other ants don't notice. At all. They walk around it as if it wasn't there, or was just an ant standing still. Three days later, they notice. If the ant is in the nest, another ant will pick up the corpse and toss it in the midden -- the outdoor garbage dump / graveyard of the ant colony. Why three days? It takes that long for the ant to start decaying to the point where it releases oleic acid. This is the smell of rotten ant, and therefore ant death: until the ant reeks of it, no other ant will notice it has died.
Likewise, if something reeks of oleic acid, it is assumed to be a dead ant even if it isn't! E.O.Wilson tested pieces of paper with oleic acid first, and they were disposed of. Then he tried taking live ants and coating them with oleic acid. As soon as they were in the nest, another ant would pick up the stinky one and throw it in the midden! The smelly ant didn't resist, but would pick itself up and clean itself off before returning to the nest ... and if it didn't do a thorough enough job, it would get thrown out in the trash again!More questions on Entomology: