The phorid fly is a tiny parasitizer.
The adult fly hovers over unsuspecting fire ants in the Southern US and Latin America and jabs its ovipositor in the ant's thorax or abdomen, laying an egg. After a while, the larva hatches and crawls to the ant's head, where it establishes itself in the brain. Gradually munching away, the 'hijacked' ant behaves abnormally at the whim of its unseen master. Eventually, it dies and the adult phorid fly climbs out, of the cognitive cockpit ready to continue the lifecycle.
This series of circular life events is very common for a wide array of flies and wasps. Natural pest experts often make use of this oddity of nature to control populations of undesirables such as aphids on roses and organic crops - where managing the balance of benificents and antagonists can lead to happiness and bountiful crops without non-decaying pesticides, which tend to stay in the ecosystem for a very long time.
The article on national geographic