October is a wonderful time of year, filled with a plethora of pumpkin spice-flavored beverages and fun Halloween celebrations. With the sun setting earlier each evening, I try to watch some of my favorite horror movies and TV shows to cultivate some holiday spirit. This past year, I was introduced to a more unique form of horror, a thrilling existential threat to human life on planet earth type of horror, in the television program called “The Last of Us”. Originally a video game franchise, the show depicts a post-apocalyptic world where a mutated Cordyceps fungus that turns people into zombies spreads like wildfire to cause societal collapse. The premise of the show is a very compelling one, especially in a post-COVID world, but the so-called “fungal apocalypse” this show depicts is very unlikely in reality. The fungi in the genus Cordyceps have evolved over long periods of time to parasitize insects and other arthropods, and many are capable of turning their host organisms into “zombies” that they can control for their own ends. In spite of the terrifying abilities of the Cordyceps, a swift shift to humans as hosts would be a longshot at best. While fungal infections and antibiotic resistance in pathogenic fungi present real issues in the modern world, the transmission of these diseases is nothing like that of the apocalyptic plot of “The Last of Us” and would not likely reach the scale of civilization’s collapse. Furthermore, many point out that the resting human body temperature of 98.6 degrees Fahrenheit is too high for many fungi to survive in, let alone adapt and proliferate in. The insects that Cordyceps fungi typically parasitize have much lower resting body temperatures than that of humans and are a more susceptible target. While the ability of fungi to turn their hosts into zombies does not quite reach the scale of our cinematic fantasies, it is still a fascinating ecological niche that illustrates the numerous interconnections within natural systems.

I was lucky enough to experience the wild and wonderful abilities of parasitic fungi in my own backyard in early 2025, a few weeks before the bulk of spring emergence had occurred. I was pacing around the backyard eagerly anticipating the frost free days to come when I noticed something strange in my small nursery plot. On a few of my seedlings I noticed that there were flies perched at the very top, motionless as if they were frozen in place. The bodies of the flies were swollen and discolored but I could not make out what had happened to them. I posted this initial encounter to my iNaturalist account to no avail, leaving me intrigued but clueless. What had caused these flies to die yet remain in place atop the plants?

Photo Credit: Dan Stevenson, ACB

Almost exactly a month later I encountered the flies perched atop my plants yet again. This time however it was a group of flies rather than just one, and each fly had fuzzy white clumps protruding from their bodies. Again they laid motionless atop my seedlings as if they had been glued to the tops of the twigs. I captured a few more photos to post on iNaturalist to see again if I could determine what on earth had happened to these flies

Photo Credit: Dan Stevenson, ACB

This next round of photos revealed that the malady these flies were suffering from was caused by species of Entomopthora, a genus of parasitic fungi that infects flies and other two winged insects. The name Entomopthora derived from the Greek words “entomon” or insect and “phthora” or destroyer, a name that could not possibly be more fitting for this organism! The pathogen infiltrates the cells of the flies bodies and siphons away water and nutrients from its cells to allow the fungi to grow. The mycelium of the Entomopthera eventually grows into the brain of the host organism and allows the fungi to control the behavior and movement of the organism. Simply put, Entomopthera turns flies into zombies and eats them from the inside out!! The fungi starts by consuming fats and other free nutrients to slowly starve the organism before consuming any of the vital organs, keeping the host alive for as long as possible. As the host organism begins to decline the fungi uses its brain controlling powers to direct the host towards a high place before it dies to ensure wider distribution of its spores to the surrounding environment. At one point a species of Entomopthora was studied as a potential biological control for common flies, but attempts at artificial cultivation of the fungi were unsuccessful.

The Zombie Fly Fungi of the genus Entomopthora, both intriguing and gruesome, offer a poignant example of just how ruthless competition can be in the natural world. One can rest assured that they won’t be turning any of us into zombies anytime soon, but they are worthy of our attention nonetheless!