Eventually the phorid fly maggot injected into an ant decapitates its host (pictured in a file photo) 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.
(See more ant photos in National Geographic magazine
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.
Photograph courtesy Sanford D. Porter, USDA