Zailo.Com!

(sorry to be a total cheat but I have cribbed the whole article) as well as the link

In South America female phorid flies have developed a bizarre reproductive strategy: They hover over fire ants

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then inject their eggs into the ants with a needle-like appendage.

The egg grows and the resulting larva generally migrates to the ant's head. The larva lives there for weeks--slurping up the brain and turning the ant into a "zombie," in some cases compelling the ant to march 55 yards (50 meters) away from its colony to avoid attack by other fire ants.

Finally the baby fly decapitates its host and hatches, exiting through the ants head, as shown in the pictures in this gallery.

U.S. scientists regularly release several species of phorid flies to control alien fire ants, which have spread across the southern U.S. during the past half century and outcompeted many native ant species.

Now scientists have released a new species of phorid, Pseudacteon obtusus (not pictured), for the first time in the U.S., Texas A&M University announced May 11. Released in southern Texas in 2008 and eastern Texas in April 2009, P. obtusus is the first phorid released in the U.S. that is known to attack ants as they forage. In theory, feeding ants are more vulnerable to attack than those hunkering down in hidden nests.

The flies which don't have a taste for native U.S. ants also drive the frightened fire ants into their nests, freeing up more food for the indigenous ants.
It's about "leveling the playing field for native ants. We're trying to restore the balance," said Rob Plowes, a research associate at the University of Texas.

Eventually the phorid fly maggot injected into an ant decapitates its host and use its hollowed-out head as a place to develop into a pupa, an intermediate stage between larva and adult fly.

Just before that, the maggot appears to control the ant's behavior, directing it to a moist, leafy place where it can emerge away from other ants that would attack.
"Not only is [the fly maggot] decapitating it, but it turns the ant into a zombie," said Sanford Porter, a research entomologist with the U.S. Department of Agriculture.
To control a fire ant invasion in the southern U.S., scientists have been releasing phorid flies into ant-infested habitats for more than a decade. Recently, Texas scientists let loose a new species of fly in Texas, which will ideally work in concert with the existing phorid species to kill a greater number the fire ants. "It certainly adds to the diversity of the impact," Porter said.

A phorid fly larvae emerges from the empty head of its fire ant host.

Fire ants first emigrated from Argentina to Mobile, Alabama, in the early 1930's probably on an agricultural-produce boat. They later spread to Texas and are still widening their range.
There's a long history of efforts to remove the ants, including physical removal and pesticides. But introducing phorid flies, which do not attack native ants, may be the most promising method so far, experts say.

About 40 days after the egg is deposited, the phorid fly larva develops into a pupa that more close resembles an adult phorid fly .

Although the flies only kill a small fraction of ants this way, the ants seem to be so afraid of the flies that their mere presence prevents the ants from collecting food, said Donald Feener, an ant ecologist at the University of Utah.
Such interruptions slowly reduce the rate at which new fire ant colonies form.
Despite successes in controlling fire ant invasions with the predatory phorid fly, it's unlikely that fire ants will be totally ousted from the southern United States, experts say. "They were still talking about complete eradication back in the early to mid 1970s," said Donald Feener, an ant ecologist at the University of Utah. "You're not going to eradicate something that is that widespread and that abundant unless you have all-out chemical warfare."B

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