The Fungi That Turn Insects Into Living Hosts

In tropical forests, a carpenter ant sometimes leaves its trail, climbs a plant stem, and clamps its jaws onto a leaf vein. It never lets go. Days later a stalk grows from the back of its head and rains spores onto the ants below. The ant has been killed, and steered, by a fungus.

What is the zombie ant fungus?

Ophiocordyceps unilateralis is a group of closely related fungi that infect carpenter ants in tropical forests, mainly in places like Brazil and Thailand. Its only goal, as National Geographic puts it, is self-propagation and dispersal. A spore lands on a foraging ant and works its way inside. Over about three weeks, according to the Penn State entomologist David Hughes in an Inverse interview, the fungus grows through the ant’s body, consuming it from within. The infection is always fatal.

What does the fungus make the ant do?

Two things, in sequence, according to the 2019 Journal of Experimental Biology paper by Colleen Mangold and colleagues. First the ant climbs vegetation, leaving the colony’s trails. Then it performs the death grip: it bites onto a leaf vein or twig and stays locked there after it dies. National Geographic describes the chosen spot as about ten inches off the ground, on the north side of the plant, a position that suits the fungus’s needs for temperature and humidity and puts the ant above the colony’s foraging routes. The fungus then kills the ant, grows a stalk from its head, and releases spores.

Only a few ants in a colony are infected at any time. One researcher told National Geographic that for the ecosystem it is less like an apocalypse than a chronic cold.

Does the fungus take over the ant’s brain?

No, and this was the surprise. For years scientists, and nature documentaries, assumed the fungus invaded the brain. In 2017 Hughes, Maridel Fredericksen, and colleagues at Penn State used electron microscopy and an image-processing algorithm to map the fungus inside infected ants in three dimensions, in a study in PNAS. They found fungal cells throughout the body, wrapped around and inside the muscles of the legs and head, but none in the brain, according to an NIH interview with the researchers. Hughes has compared the fungus to a puppeteer pulling strings: it seems to control the ant’s muscles directly rather than through the nervous system.

The 2019 follow-up looked at the jaw muscles during the death grip. The muscles were extensively colonized and showed signs of hypercontraction and damage to their membranes, yet the motor neurons and the junctions between nerve and muscle appeared intact. The authors suggest the fungus secretes compounds that cause the muscles to contract. How the climbing behavior is triggered remains unknown.

Why would the fungus spare the brain?

Hughes has speculated that the fungus needs the ant alive and able to climb and bite until the last moment, so it keeps the brain working while it dismantles the rest. He told Inverse that the fungus releases chemicals that appear to protect the brain even as surrounding tissue breaks down. That is a hypothesis.

Are there other fungi like this?

Several. Entomophthora muscae, whose name means insect destroyer of the fly, makes infected flies climb, glue their mouthparts to a plant, and die with the abdomen raised, a pose that helps spores spread, according to National Geographic. Massospora cicadina infects periodical cicadas, causes part of the abdomen to fall away, and produces psychoactive compounds; the infected cicadas keep flying and mating, spreading spores. Hughes notes that caterpillars, moths, and beetles are also infected by this group of fungi, but the dramatic behavioral manipulation shows up mainly in ants and wasps.

Could this happen to people?

No. These fungi are specialized to particular insect hosts, and nothing in the research suggests they could infect a mammal. The video game and television series The Last of Us, which Hughes consulted on, imagined a human-infecting cordyceps, and he has been clear that the real fungus stops well short of that.

What does this have to do with death?

The zombie ant is one of the clearest examples in nature of death being used by another organism: the fungus needs the ant’s death to happen in a particular place and posture, and shapes its behavior to arrange it. It is also a reminder that most of what happens to a body after death is the work of fungi and microbes, which is the ordinary end of the story for every animal. See what happens to your bones after burial and do animals understand death.

This is general educational information, not medical advice. Research in this area moves quickly and this page reflects sources available at the date shown; check the date and the sources before relying on a specific claim.