Attack of the Zombie Ants!

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While we may be unsure about the existence of ghosts, the Bruce Science Department can be much more decisive on zombies: They exist! Zombie ants, that is.

There is a species of fungus, Ophiocordyceps unilateralis, which is capable of infecting ants and turning them into biological zombies, acting according to the fungus’ needs instead of their own.

When an ant is infected by Ophiocordyceps spores, the fungus begins to grow throughout its body. At first, isolated fungal cells drift and multiply in the ant’s hemolymph, a fluid that is analogous to blood in vertebrates. As the infection progresses, the fungal cells form tubules, creating an interconnected network in the ant’s body that allows for swift growth and nutrient transfer.

The fungal network inserts its cells into almost every part of the ant. As the ant’s muscles become invaded by fungal tubules, the fungus is able to truly take over and manipulate the hapless arthropod. At this point, the ant could almost be considered “fungus in ant’s clothing.” Interestingly, though there is a high concentration of fungal cells outside the brain, they do not penetrate it. Perhaps the fungus needs the ant brain left intact for the ant to survive its final mission.

 Image by David P. Hughes and Maj-Britt Pontoppidan.

Image by David P. Hughes and Maj-Britt Pontoppidan.

The infected ant will leave the safety of its nest and find a plant to climb. It will stop at a height of about 25 cm (9.8 inches) where the temperature and humidity is best for the fungus to grow. Then, the fungus will force the ant to take one final action: Latch its mandibles onto the underside of a sturdy leaf or twig. There the ant’s body will remain as a bulbous-headed stalk erupts out of its head.

Before long, the capsule bursts open and releases spores. Infected ants generally climb plants near foraging trails, and the ants passing beneath may become infected themselves. Soon, more zombie ants emerge to climb stalks, disperse spores, and spread the infection.

How does the fungus so completely control the ants’ behavior? Science has yet to find an answer. However, what researchers have found is that Ophiocordyceps can chemically alter the brain and change gene expression, possibly leading to some of the behavioral changes.

Does the description of this fungus sound familiar to you? It is so creepy, that it has served as the basis for zombie diseases in a variety of media, including the book (and later, film) “The Girl with All the Gifts”, and the video game, “The Last of Us.”

Ophiocordyceps may seem like a horror of nature with no real purpose, but it could actually be useful for humans. Preliminary results suggest it could be used to treat malaria. It also has promise as a food coloring, and as a component for tuberculosis tests. Humans and insects are very different biologically, so it is incredibly unlikely that Ophiocordyceps will be infecting humans anytime soon. Still, it could become a part of our lives nonetheless!

Kate Dzikiewicz, Paul Griswold Howes Fellow