Fly Pirates rob Droptail Ants

Two days ago I was surprised to see flies of the genus Bengalia robbing false army ants of their larvae. Then I noticed that wherever there were ants of any species collecting food, there were Fly Pirates in attendance. The flies were robbing ants of whatever they picked up: Bits of flowers, seeds, or any organic material. Since there seemed to be an abundance of such snacks lying around on the forest floor, I started wondering why the flies couldn't simply gather their own food. Perhaps the flies saved labour by letting the ants discern edible stuff from the rest. So I ran a little experiment. What if I presented the flies with something that was obviously a good meal, like grated cheese?

So I placed some cheese within view/smell of the flies. No reaction!
In no time at all some droptail ants started breaking up the cheese gratings for easier transport back to their nest. The flies observed but kept their distance.

OBSERVATION: The flies ONLY become interested once the ants start carrying the cheese cuttings.
Before that, the flies observed the ants intently. At one stage a fly perched atop a passing duo of Toktokkies (busy trying to sort out their reproductive plumbing), enjoying a touring view of the feasting place. There were ample bits of cheese unattended, close to the flies, but their interest was focused only on the ants. Once an ant started moving a piece of cheese, a fly or two would start harassing it. Sometimes a tug of war ensued and sometimes the ant would let go and charge the fly, which then retreated. On some occasions the fly would take the fight into the air, gripping the cheese with its forelegs trying to shake the ants off. If that failed, it would drop the ant and cheese quite violently to the ground and then try and separate cheese from ant. On some occasions the fly would simply start feeding on a chunk of cheese while the ant was underway, not trying to separate it from the ant. The irritated ant would then drop the cheese and shoo the fly away (see gif animation).

What struck me was that the flies treated the droptails with less respect than the false army ants. The droptails have stingers, no? The false army ants have no stingers and are blind, but seem to have powerful mandibles and are quick movers.