In 2023, researchers uncovered new insights into the eerie world of fungi that transform insects into "zombies." Carolyn Elya, a molecular biologist at Harvard, along with her coworkers, demonstrated that the fungus Entomophthora muscae may secrete substances into the hemolymph of fruit flies, allowing it to manipulate their neurons. This discovery sheds light on how parasitic fungi can control the behavior of their insect hosts.
Elya's fascination with Entomophthora muscae began when she discovered zombified fruit flies in her backyard while she was a PhD student at UC Berkeley. She had put out rotten fruit to attract wild fruit flies and found dead ones with wings raised and white fuzzy spores on their abdomens. Sequencing the DNA from the spores confirmed that the flies were victims of Entomophthora muscae.
Intrigued by this phenomenon, Elya infected Drosophila melanogaster, a well-established lab model, with Entomophthora muscae to study the fly brain and understand the manipulation. In her 2023 report, she and her team showed that the fungus could be secreting something into the fly's hemolymph that helps manipulate neurons. When Elya injected hemolymph from infected flies into uninfected ones, the latter started behaving as though they had been zombified.
Similarly, Sam Edwards, a postdoctoral researcher at Wageningen University, along with Henrik H. De Fine Licht, an evolutionary biologist at the University of Copenhagen, and colleagues reported their analysis of RNA in house fly heads after E. muscae infection. They detected activity of a fungal gene similar to one called egt, present in zombifying viruses that force infected caterpillars to move to high locations. They hypothesize that this gene in E. muscae might induce summiting behavior in infected flies.
The work of Elya, De Fine Licht, and others has advanced understanding of how parasitic fungi control insect behavior. Their research suggests that Entomophthora muscae may directly release chemicals that activate neurons involved in the fly's summiting behavior. Alternatively, the fungus's presence and physiological changes in the fly may trigger the fly's own neurons to release chemicals that start the process.
Entomophthora muscae is not alone in its macabre manipulation of insects. Cordyceps fungi, including species like Ophiocordyceps unilateralis, are famous for hijacking the brains of ants. Once a Cordyceps fungus takes over an ant, it directs the ant to climb to a high point on a plant and then bite down on the stem or twig in a macabre death grip, a behavior called "summit" or "death grip." The reproductive structures of the Cordyceps fungus will soon burst out of the ant's head, spreading its spores to infect another unsuspecting host.
In the real world, ants usually come into contact with Ophiocordyceps unilateralis when spores fall on them from a tree or plant above. The spores penetrate the ant's body without killing it, and the fungus infiltrates the exoskeleton or digestive tract of the insect with a thin, needle-like tube. The fungus then changes to a new phase and consumes the ant's organs, including its brain. The spores fall on healthy ants below, starting the cycle again.
Similarly, Cordyceps gunnii attacks caterpillars such as large "ghost" caterpillars in Australia. Unlike the ant-infecting Cordyceps, Cordyceps gunnii does not force its victims to climb but takes control when they are buried in the soil. The fungus produces very fine threads (hyphae) that spread through the body of the insect, replacing its structure. The caterpillar is doomed as soon as the Cordyceps fungus starts to grow inside it.
Eventually, the fungus pushes antler-like reproductive structures out through the caterpillar's head, and a stalk sprouts from the head of the dead insect, producing spores. These spore-producing structures can be more than 10 centimeters long. Wind carries the spores to infect more unwary caterpillars.
The horrifying capabilities of Cordyceps fungi have inspired popular culture, notably the zombie-apocalypse video game and TV series "The Last of Us." In "The Last of Us," a widespread fungal infection turns people into zombie-like creatures and causes the collapse of society. However, in reality, humans have nothing to fear from Cordyceps fungi. "Despite their depiction in 'The Last of Us', humans have nothing to worry about from Cordyceps fungi."
Fungi like Cordyceps are highly specialized and have evolved over millions of years to infect specific insect hosts. A fungus that specializes in infecting and controlling ants or cicadas would need to develop enormously new tools over millions of years to infect even another insect, much less a human. Not all fungi are scary, and even the most alarming ones will not turn you into a zombie.
Some species of Cordyceps have been used in traditional medicine for centuries. Cordyceps sinensis, a Chinese vegetable caterpillar very similar to Cordyceps gunnii, has been used in traditional medicine. Modern research shows there may be benefits from its use (or extracts from it) in treatments associated with autoimmune responses.
Sources: The Conversation, Popular Science, El Sol de México
This article was written in collaboration with generative AI company Alchemiq