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.")
Watch a fly make away with an ant's head.
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."
Other phorid flies from South America also practice ant decapitation, but using a completely different method.
Species including Pseudacteon obtusus inject their eggs into an ant's body. After the fly maggot hatches, it burrows its way to the ant's head and starts eating the contents.
Once hollowed out, the head pops off, providing the maggot the perfect place to pupate and turn into an adult. (Also see "Pictures: 'Zombie' Ants Controlled, Decapitated by Flies.")
As for whether the maggot controls the ant's behavior by getting inside its head, like other parasites do, "nobody really knows," Brown said. "We haven't studied these flies very well."
Deadly Dung Beetles
Among dung beetles there are also some unexpectedly dedicated headhunters.
One such dung-eater turned predator is Canthon virens, a species that hunts down queen leafcutter ants.
In a behavior first reported from Brazil in 2012, a female beetle pounces from above and, after a tussle, beheads the queen.
The female beetle then rolls the head away and proceeds to bury not only itself and its prize, but also a male suitor—a process that takes up to 12 hours. Eggs are laid, and the queen ant's head becomes an underground larder for the beetle young.
If ants seem to be unfairly targeted, consider another dung beetle, Deltochilum valgum, that specializes in decapitating millipedes. (Related: "Carnivorous Dung Beetle Shuns Dung and Decapitates Millipedes.")
The armored insect, found in Central America, delivers the coup de grâce by sawing between the millipede's body segments while forcing up its victim's head—usually making it pop off.
Headless Mantis Sex
Praying mantises are perhaps the best known insects to go for the head—particularly during sex.
Females of species such as the European mantis (Mantis religiosa) are liable to chew off their mate's head during copulation. (Watch a video of praying mantises mating.)
Not that this appears to affect the male's performance—quite the reverse, in fact, according to William Brown, a biologist at the State University of New York at Fredonia.
Decapitation severs a nerve in the male that actually removes its sexual restraint.
"So once their head is off, males vigorously attempt to mate with the female," Brown said in an email.
"Males can live for hours after decapitation and are very adept at copulating successfully."
The female gets a free meal into the bargain, but why the head? (Also see "Fireflies Are 'Cannibals'—And More Surprising Facts About the Summertime Insect.")
"Decapitation occurs first because of convenience," Brown said. "Males either approach a female head-on or, once mounted, they turn to align head-first with the female."
In the case of the Japanese giant hornet (Vespa mandarinia japonica), beheadings are used as a means to get a meal.
Watch a video of these "hornets from hell."
When raiding beehives for their honey and larvae, these ferocious insects first have to get past thousands of adult bees that defend the hive with their lives.
Slicing through the defenders with their powerful jaws, a raiding party of just 30 giant hornets can wipe out a colony of 30,000 bees in a few hours.
Now that's what you call efficiency.