When it comes to the ruthless headhunters of the insect world, looks can be deceptive.

Take the tiny, seemingly unassuming tropical flies that make their living by slicing the heads off ants, as reported this month in Biodiversity Data Journal.

In the new study, scientists recorded three species of phorid flies, from the poorly known Dohrniphora genus, decapitating trap-jaw ants in the forests of Brazil and Costa Rica. (Related: "There's More Than One Way to Decapitate an Ant.")

The previously unknown behavior was caught on camera by a team led by Brian Brown, curator of entomology at the Natural History Museum of Los Angeles County.

A female fly uses a superlong proboscis tipped with a bladed cutting organ to surgically remove the victim's head. The fly then drags the head away and either feeds on the goo and brain or lays an egg inside.

"The head certainly makes a nice little shell for the larva to develop in, so that may be the reason why they actually go for the heads," Brown said. (Also see "7 Bug and Spider Myths Squashed.")

The flies cleverly avoid being crushed by the much larger trap-jaw ants by targeting ants injured during colony battles, he explained.

Brown said the mini-surgeons sniff out their maimed victims using "the alarm pheromones the ants produce when they are fighting."

Keep reading for more brutal decapitators: To quote England's King Henry XIII, "Heads will roll."

Head-Popping Flies

Read more:

Heads Will Roll: 5 of Nature's Most Brutal Bug Decapitators