Biology

Stranger than Fiction: Zombies in the Natural World

By Aditya Nair

You don’t need to be a board-certified physician to diagnose the nation with zombie fever. The Walking Dead. Left for Dead. Dead Set. Shaun of the Dead. Zombieland. Countless zombie Halloween outfits. There’s no denying it: our nation is obsessed with zombies.

The concept of the possessed, brainless, half-living deformed creatures roaming the earth may seem to be purely a product of human imagination, yet this may not be too far from the reality of the natural world.

Meet the Cordyceps fungus, a genus of fungus that has evolved one extremely special trait: mind control. One species closely related to this genus is Ophiocordyceps unilateralis. Upon infecting an ant, the fungus heads straight for the ant’s brain and compels the ant to break from the rest of its colony. It directs the ant, in an astoundingly intricate and specific manner, to travel to the underside of a leaf that is facing north-northwest at around solar noon. The “zombie ant” then clamps down on the leaf with its powerful mandibles, a sort of rigor mortis before the ant is even dead. It will never again move from this position.

Now that the fungus has reached its destination, where temperature and humidity conditions are ideal, a stalk emerges from the dead ant’s head, a deadly skyscraper towering into the jungle air. Then, as if this wasn’t weird enough, the tip of the stalk eventually ruptures and spews clusters of fungus spores into the air from its high-altitude position. These clusters then explode mid-flight, showering the jungle floor (and unsuspecting, innocent ants) with more fungus spores. If an ant is unlucky enough to be “rained on” in this way, the spore will attach itself to the exoskeleton of the ant and slowly build up enough pressure to rupture the exoskeleton, perpetuating the cycle.

The Cordyceps fungus controls the mind of its host and then emerges from its head. (via The Last of Us wiki)

However, evolution isn’t done yet: the ants have their own ways of fighting back. If an uninfected colony ant notices the telltale weird behavior of an infected ant, the healthy ant and some friends will carry the stricken ant as far away from the colony as it can and dump the zombie somewhere where it can no longer hurt the colony.

To top it all off, scientists have recently discovered another unidentified fungus that infects Ophiocordyceps unilateralis. That’s right – this unknown fungus’ evolutionary role is to infect another fungus (fungus-ception?). Upon infection, only 6-7% of the spores of unilateralis are viable, checking its potential spread and protecting ant colonies from excessive destruction.

From fossil evidence, scientists think that zombie fungi such as these have been around for 48 million years. Here we have a testament to the power and creativity of evolution that can capture our own imaginations. In fact, in the hit video game The Last of Us, humankind is afflicted with a mutated form of this fungus.

Once again, nature’s imagination has proven to be much more elegant, beautiful, and complex than our own.

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