I've heard some folks insist that it does. Of course, they were in the business of selling DE. Maybe they had enough of it to really affect the ants, maybe they just wanted to help their business. I found it too expensive to spread over the fire ants. Plus, there are many different sub-species of fire ants, some products are more/less effective on them.
I've found that 5% Sevin Dust spread around the nest can kill the ants. My favorite remedy is pouring boiling water over the mound.
DE will displace them, they usually pop up somewhere else. If you have 2 or more mounds, take your shovel and scoop up one mound and dump it on a different mound. The fire ants will fight to the death.
I sprinkled DE around 3 huge mounds last week without disturbing them. Took about 2 days and the mounds were empty. I don't know if the ants died or abandoned the mound, but they were gone. No sign of them anywhere else in the yard.
Boric acid has been used to kill a wide variety of insects in various situations for many years. It can be mixed with sugar or syrup to make a household ant bait as well. In a laboratory study, four dilutions of boric acid (.25%, .50%, .75% and 1%) were mixed with sugar water and offered as a bait to treat fire ant mounds. All dilutions achieved 95 to 100% control within 8 weeks. (14) Bushwhacker
is an 18% boric acid granular bait that is registered for fire ants. A new gel bait containing orthoboric acid, called Drax Nutrabait, came on the market in July 2003. It is available from the Waterbury Company.
Boric acid is a white, inorganic powder chemically derived from water and boron, which is mined from vast mineral deposits in the ground and used in consumer products such as laundry additives, toothpaste and mouthwash. Deadly to cockroaches, boric acid is low in toxicity to people and pets, and is even used as an eyewash albeit in a 1% water solution. It is also odorless and contains no volatile solvents. Boric acid has been a favorite weapon against ants and roaches for more than a century, and is one of the most effective cockroach control agents ever developed, provided that it is used correctly. CAUTION: It should be kept away from children and pets
DE can kill fire ants and any other type of ant. Under some circumstances.
The key thing is that it has to be DRY in order to work. Once it gets wet it loses effectiveness until it dries out and is fluffed up again.
At this time of year here in Florida it would be about worthless to spread it on a fire ant mound. It rains too much. In April and May it would be more effective when it may not rain for a couple of weeks or more.
Where I find it useful is in my nest boxes, inside the roost houses, and in my feed storage room. I powder nests and floors liberally with the stuff twice a year or so and it works well for keeping ants and roaches under control.
But out in the yard where it will be rained on it's worthless.