But first a little background on the fire ant, specifically the Red Imported Fire Ant. This ant is native to South America. Back in the 30's it hitched a ride on some cargo ships from Brazil and wound up in Mobile, AL. You've probably seen horror movies where fire ants crawl all over people and sting them to death. They are definitely a pest to be eradicated.
Fortunately, intrepid entomologists have discovered that fire ants have a natural enemy in the phorid fly, specifically the genus Pseudacteon. Here's what happens:
Poor Mr. Fire Ant is attacked by Mrs. Phorid Fly, who injects her eggs into the ant. Unfortunately for the fire ants, they do recognize the flies as enemies. Anthropomorphically speaking, this ant seems to know what's in store for him.
When the fly egg hatches, the larva burrows into the ant's head. It slowly munches away at the brain, causing the ant to wander aimlessly. When it is time for the larva to pupate, it releases an enzyme that causes the ant's head to fall off. Thump.