Watch Out for Zombies! At Least, in Fungus Form…

A bizarre fungus that infects different kinds of insect can cause strange behavior — and frightening alterations to their bodies.
by Mike Dunn

October means football, cool temperatures, colorful leaves and our spookiest holiday of the year – Halloween. Befitting that theme, I made a bizarre discovery in my yard one Halloween a few years ago.

I was walking around the yard looking for something to photograph when my eye caught a strange shape on the underside of a twig. I moved over for a closer look. It was a spiky, insect-shaped corpse, a cricket of some sort, I thought. I recognized the strange growth forms on its body as some sort of parasitic fungus, one of the most Halloween-appropriate things in nature.

After some research, I figured my little corpse was a Carolina Leaf-roller, a type of wingless cricket. If that was the case, then this fungus was probably a species of Cordyceps (or perhaps Ophiocordyceps), a group of fungi that attack various insects. These insect-eating fungi have been collectively called Zombie Fungi for the way they infect and ultimately kill their hosts. 

Research is uncovering more about how these entomopathogenic (insect-infecting) fungi function. A passing insect encounters a fungal spore in its wanderings that gets attached to the outside of its body, where it germinates. The fungus then penetrates the exoskeleton using enzymes or a needle-like peg that presses against the cuticle and punctures it. Once inside, the fungus starts to grow and absorb nutrients from its host. 

As if that wasn’t strange enough, now things start to get really weird.

Within a few days after infection, the host insect begins to behave differently due to chemicals secreted into its brain by the invading fungus. Studies have shown that ants infected by one species of zombie fungus tend to crawl up on vegetation and lock onto a leaf with their mandibles. They soon die, and strange, stalk-like structures grow out of the ant to release spores. By altering the behavior of the ant to make it climb up off the ground and attach its soon-to-be-dead body to the vegetation, the fungus ensures its spores are released in an environment favorable to their dispersal by wind.

The same is probably true of my dead cricket. It had been manipulated into a good spore-release position on the underside of a twig a couple of feet above the ground. I can’t say whether the cricket was tricked into clasping the twig with its legs or if it was stuck in place by another mechanism seen in some body-snatching fungi — when specialized cells burst through the legs and other body parts of the victim to anchor the hapless host.

Other parasitic fungi infect many other types of invertebrates. I have found flies in many areas across our state stuck in odd positions on plants, with white fuzz coming out between their abdominal segments. This type of fungus has been well-studied in fruit flies, where scientists have tediously mapped out the nervous system of these flies for various experiments. It seems this fungus takes over the brain of the fly, causing it to climb to a high point in its environment (a process called “summiting”) and then glue itself to the plant with secretions from its “tongue.” The spores of the fungus are then shot out like miniature rockets ready to infect another passing fly.

Then there was the time I found a bunch of dead soldier beetles in a patch of goldenrod flowers. They were all grasping onto the flowers with their mandibles in an odd death grip, wings cocked open, with a whitish fuzz on their abdomens. From what I have read, this is most likely the work of a fungal pathogen called Eryniopsis lampyridarum, a specialist on these beetles.

One scientist studying this cleverly dubbed the infected insects “zombeetles.” He noted that by some as-yet-unknown mechanism, several hours after the beetle dies, the fungus manipulates the beetle’s wings to open up and hold that position. Unlike the rocketing fly-fungus spores, this one apparently needs another beetle to touch its dead comrade to become infected. This open-wing position increases surface area for body contact and seems to attract other beetles in what he described as faux mating behavior.

The more I learned about these fungi, it started me thinking about the what-ifs of this ghastly group. Apparently, I’m not the only one. It turns out these fungi served as the inspiration for an award-winning video game and now a popular television show, The Last of Us. The story explores the concept of the Cordyceps fungus evolving and infecting humans. A classic case of truth being stranger than (or at least inspiring) fiction. 

So if you notice a neighbor with odd-stalk-like projections coming out of their backs as you go about your trick-or-treating this year, you may want to skip that house. 

This article originally appeared in the October 2024 issue of WALTER magazine