Parasitic ‘Last of Us’ fungus turns reclusive arachnids into living dead

By Balambal Suryanarayanan

This “serial killer” fungus — Gibeiulla attenboroughii — appears as a white, prickly, mesh-like substance that spreads over its arachnid victims and forces them to move out into the open. **Jenna El-Attar/** Guest Artist

In 2019, a parasitic species from the genus of the Cordyceps fungi invaded and spread through the bodies of unsuspecting ants, exerting control over the infected ants like a Dungeons and Dragons Mind Flayer would. The fungi, named Ophiocordyceps unilateralis, grows inside the ant host, and first manipulates them into climbing a peak. It then attacks the mandibles of the ant to damage the muscle fibres, forcing the muscles to contract and making them swollen. Once the ant’s mandibles can no longer move, the fungus bursts out of its body through the head and showers spores upon the other members of the family of ants that might have unfortunately ventured off near the peaks.

The horrifying thing that scientists discovered was that these ants could be described as undead, but not because the fungus controlled the brains of these ants. Instead, the fungi acted as part serial killer and part puppet master. Like a serial killer, they carried the exoskeletons of dead ants like trophies, moving them away from their colonies. Like a puppet master, they made the dead ants seem as if they’re moving like zombies, though it was just this malevolent, microscopic fungi pulling the strings. And then, the fungi grows bored of one dead ant and sets off to hunt for more.

What surprised avid naturalists was that the interaction between the ant and the fungi did resemble a defense mechanism against the “serial killer,” with the ant fighting back and leaving its DNA (or the ants’ beady body parts) with the fungi. The world’s introduction to the idea of parasitic fungi was fueled by Naughty Dog’s “The Last of Us,” released in 2013. The HBO adaptation of the show, a critically acclaimed post-apocalyptic drama, furthered knowledge of the fungus.

Two years after the discovery of Ophiocordyceps unilateralis, an abandoned gunpowder storage shed in Belfast welcomed a BBC team filming an episode of “Winterwatch,” inadvertently introducing them to the next serial killer fungus that appeared as a white, prickly, mesh-like substance spread over dead spiders on the roof. Dr. Harry Evans, an emeritus fellow at the Centre for Agriculture and Biosciences International, received an image of the enmeshed creatures. He hypothesized that they might be distantly related to O. unilateralis and that the species would need to be studied to better understand the way they functioned and killed cave spiders.

Research into the spiders hunted by the new species of fungi revealed that both the spiders, metardi and merianae, belonged to the Metellina genus of orb-weaving spiders. Naturalists have long known these spiders to be highly reclusive creatures, spending most of their time hiding near their webs inside damp caves or man-made dilapidated cellars filled with moss and lichens. Tim Fogg, a well-known cave explorer, fascinated and intrigued by the spores, reached out to Evans with similarly infected specimens of the Metellina metardi species of arachnids. In a conversation, he admitted that “the end was sad for the spiders.”

With the recent publication of the work of Evans, Fogg, and Dr. João Araújo in the journal Fungal Systematics and Evolution (FUSE), Dr. Araújo, a curator of mycology at the Denmark History and Natural Museum, explained how this fungal species targets reclusive spiders. First, the fungus lands on the spiders and sprouts a germ tube — a root-like structure that transforms into a drilling machine to penetrate the spiders’ exoskeleton (outer covering). Fungi thrive in environments that are damp, dark, and rich in proteins and organic nutrients, and the spiders’ exoskeletons, packed with chitin (a protein responsible for their hard shells) and wax, serve the perfect feast for the fungi on a silver platter.

Once inside, the fungus starts to multiply through asexual reproduction. First by multiple fission and budding within the body of the spider, and then it bursts out as spores. Araújo added that the interior of the arachnid’s body is replaced by a spider-shaped mass of the fungus, resembling the Zygomind from “Volo’s Guide to Monsters,” a terrifying monster that turns its hosts into spore-controlled husks. Steadily, the fungus manipulates the spider by a mechanism that remains enigmatic to Araújo, Fogg, and Evans, even though some research suggests that it resembles the behavior of the Cordyceps fungi. The fungus may flood the host with the reward hormone dopamine, changing the spider’s behavior by making them move away from their reclusive spots into the open space, high on rooftops and cliffs where they can easily burst out of the spider bodies, mimicking the killer behavior of the Cordyceps fungi.

Evans says that the spider might not realize that their organs are shutting down and that they are not moving; instead, they’re just slaves of these fungi which control their movements. Fogg mentioned that from studying parasites, autotrophs, and symbiosis, we’ve come a long way to learn about zombification in nature.

Evans has since christened these fungi Gibeilulla attenboroughii, after the acclaimed naturalist David Attenborough, the founder of the “Planet Earth” series who has played a huge role in the discovery and analysis of fungal species.

Mackinnon, an ecologist studying fungi in British Columbia supported Dr. Evans’ findings, emphasizing that these fungi don’t pose a threat to humans. They don’t go prowling on people like zombies do; instead, they play a major role in regulating the food chain by zombifying the arachnids and keeping their species in check. Dr. Evans is optimistic about the potential applications of these findings in developing “zombie organs” in organ transplantation and biomedicine. He hopes to explore how these fungi can develop more immune-resistant organs that were once administered using cyclosporine.

Nevertheless, people with arachnophobia (the fear of spiders) and kinemortophobia (the fear of zombies) need not be terrified as these spiders don’t jump on humans, nor are the fungi tempted to unleash terror on the humankind. Consequently, zombie-land is safe, within the confines and creative minds of writers and editors, at least for now.