Matt Kasson: Zombies strike fear into our hearts – and if they persist, they eventually end up in our heads. Animals taken over by zombies no longer have control over their own bodies or behavior. Instead, they serve the interests of a master, whether it is a virus, fungus, or other harmful agent.
The term “zombi” comes from Vodou, a religion that originated in the Caribbean country of Haiti. But the idea of armies of undead, brain-eating human zombies comes from movies like “Night of the Living Dead,” television shows like “The Walking Dead” and video games like Resident Evil.
These are all fictional. In nature we can find real examples of zombification: one organism controls the behavior of another organism.
I study fungi, a vast biological kingdom that includes mold, mildew, yeast, mushrooms, and zombifying fungi. Don’t worry: these “brain-eating organisms” tend to target insects.
Insect body robbers
One of the best-known examples is the zombie ant fungus, Ophiocordyceps unilateralis, which is part of a larger group known as Cordyceps fungi. This fungus inspired the video game and HBO series “The Last of Us,” in which a widespread fungal infection turns people into zombie-like creatures and society collapses.
In the real world, ants usually come into contact with this fungus when spores – reproductive particles the size of pollen that the fungus produces – fall onto the ant from a tree or plant above the ant. The spores enter the ant’s body without killing it.
Once inside, the mold spreads in the form of a yeast. The ant stops communicating with nest mates and staggers around aimlessly. Eventually it becomes hyperactive.
Finally, the fungus causes the ant to climb a plant and cling to a leaf or stem with its jaws – a behavior called toping. The fungus enters a new phase and consumes the ant’s organs, including the brain. A stalk erupts from the dead insect’s head and produces spores, which fall onto healthy ants below, starting the cycle again.
Scientists have described numerous species of Ophiocordyceps. They are all small and have very specialized lifestyles. Some live only in specific areas: for example, Ophiocordyceps salganeicola, a parasite of social cockroaches, is only found in Japan’s Ryukyu Islands. I expect there are many more species waiting to be discovered worldwide.
The zombie cicada fungus, Massospora cicadina, has also received a lot of attention in recent years. It infects and controls periodical crickets, which are crickets that live underground and emerge briefly to mate in cycles of 13 or 17 years.
The fungus keeps the crickets energetic and flying around, even as it eats and replaces their rear ends and abdominal muscles. This long-term “active host” behavior is rare in fungi that invade insects.
Massospora has relatives that target flies, moths, centipedes and soldier beetles, but they cause their hosts to surface and die, such as ants affected by Ophiocordyceps.
The real mold threats
These various pathological partnerships – relationships that lead to death – were formed and refined over millions of years of evolutionary time.
A fungus that specializes in infecting and controlling ants or crickets would have to develop vastly new tools over millions of years to be able to infect even another insect, even a closely related one, let alone a human .
In my research, I have collected and treated hundreds of living and dead zombie crickets, as well as countless fungus-infected insects, spiders, and centipedes. I have dissected hundreds of specimens and uncovered fascinating aspects of their biology. Despite this prolonged exposure, I still have control over my own behavior.
Some fungi threaten human health. Examples include Aspergillus fumigatus and Cryptococcus neoformans, both of which can invade people’s lungs and cause severe pneumonia-like symptoms.
Cryptococcus neoformans can spread beyond the lungs to the central nervous system and cause symptoms such as neck stiffness, vomiting, and sensitivity to light.
Invasive fungal diseases are increasing worldwide. This also applies to common fungal infections, such as athlete’s foot (a rash between your toes) and ringworm, a rash that, despite the name, is caused by a fungus.
Fungi thrive in consistently warm and wet environments. You can protect yourself from many of them by showering after getting sweaty or dirty and not sharing exercise clothes or towels with other people.
Not all fungi are scary, and even the alarming ones won’t turn you into a walking dead. The closest you’ll come to a zombifying fungus is by watching scary movies or playing video games.
If you’re lucky, you might find a zombie ant or fly in your own neighborhood. And if you think they’re cool, you can become a scientist like me and spend your life looking for them.
Matt Kasson, associate professor of mycology and plant pathology, West Virginia University
This article is republished from The conversation under a Creative Commons license. Read the original article.
