Buzz
Phorid flies may be small—most are tiny enough to perch on your pinky nail with room to spare—but they belong to a vast family. Over 4,000 phorid species exist, and their ways of life are remarkably varied. Some are herbivores, others predators, scavengers, or parasites. Many are just a little unsettling.
Take the so-called 'coffin flies,' which thrive in decaying plant material and carrion, including bodies in caskets. Then, there are the 'ant-decapitating flies.' These species lay their eggs into dying ants. When the larvae hatch, they wriggle toward the ant’s head, devour its brain and anything else they can find, and eventually eat so much that the head detaches from the body.
That’s the usual method. However, scientists have recently discovered some ant-decapitating flies that follow a completely different approach—one never seen before in nature.
Entomologists Brian Brown, Giar-Ann Kung, and Wendy Porras have spent years studying phorids and have gathered thousands of specimens from eight different countries. On a recent research trip in Brazil, a fly did something that even surprised them. While they were observing ants as bait and waiting for a particular fly to appear, Kung witnessed an unexpected scene: a fly landed on an ant, severed its head, and flew off with the trophy. The team was amazed. In every other species of ant-decapitating phorid, it’s the larvae that perform the beheading, eating the inside of the ant’s head. But here was an adult fly doing the job and flying off with the head afterward.
After further exploration in Brazil and Costa Rica, the researchers identified three species displaying this 'headhunting' behavior. Here’s how it unfolds: A male and female fly arrive at an injured ant together, often mid-flight while mating. Upon landing, the male departs, leaving the female to examine the ant. She circles around it, tapping the ground and occasionally approaching to poke the ant or tug on its antennae or legs, gauging how vulnerable it is. If the ant doesn’t resist, the female mounts it and begins stabbing just behind the head with her mouthparts. Her proboscis, nearly as long as her body, ends with a spike and two serrated blades. She jabs them into the ant repeatedly from different angles, twisting her head to sever the nerves, digestive tract, and the membrane connecting the head to the thorax.
After just eight minutes of this action, the head becomes loose enough for the fly to detach it with a strong pull and carry it away. What she does with it remains uncertain. Typically, an ant carcass serves as a nursery for phorid flies, but the researchers saw only a few flies lay eggs in the ants, and some dissected ants contained no eggs at all. If the head or headless body isn’t used for laying eggs, it’s likely a meal. Some of the flies studied by Brown, Kung, and Porras fed on the collected heads, and the researchers believe these heads provide the nutrients needed for the flies to develop their eggs.
Despite their gruesome feeding habits, these flies are selective eaters. The researchers found that the headhunting phorids targeted only trap-jaw ants, ignoring other injured insects placed before them. By specializing in decapitating this one species, they might be carving out a niche in an ecosystem overflowing with flies and other insects that parasitize and feed on ants.
