Zombie Flies
This past weekend, I visited my family in Pennsylvania, and we went hiking in the Catskills, where my dad volunteers as a trail steward. We hiked through a dense hardwood forest, a very classic northeastern trail experience. It felt like trails I had hiked for years, but at the top I saw something I had never seen before.
When we reached the summit, we stopped at a picnic table for lunch. Someone mentioned the unusually large number of flies buzzing around. I wondered if animal scat nearby was to blame. Not being a fly expert, I shrugged it off and tried to ignore the constant buzzing.
After enjoying some peanut butter and jelly sandwiches, we climbed the fire tower that overlooks the Catskills. The trail steward on duty pointed out Hunter Mountain, Slide Mountain, and helped orient us to the landscape. Afterward, we began to prepare for our descent.
While waiting at the trailhead for my dad to finish packing his bag, I glanced down at the tall grass lining the dirt path. That’s when I noticed something strange: a fly clinging to the very tip of a blade of grass. Its wings were outstretched, giving the impression it was alive, yet it remained motionless. Curious, I gently reached for the blade of grass. Still no movement. The fly was clearly dead but in such a specific, almost posed position.
Fly hanging onto blade of grass with wings outstretched.
Then I stepped back and looked again.
The entire grassy area was speckled with flies just like it, all clinging to the tips of grass blades. On closer inspection, I saw white fuzz emerging from their abdomens. Had they died here and started to decompose?
Family members tossed around theories—egg sacs? galls?
…But I (usually) know a fungus when I see one.
Entomophthora muscae fungi emerging from fly’s abdomen.
When I see something intriguing I have not seen before in nature, I feel a kind of competitive drive to learn everything I can about it. So, I got to work researching as soon as I got home.
I had witnessed the work of Entomophthora—Latin for 'insect destroyer'—a parasitic fungus that targets various insects. Entomophthora muscae is a species that infects only flies. Unlike what I first assumed, the fungus doesn’t infect dead flies. It attacks while they’re alive. It’s often called “zombie fungi.”
Once inside the body, the fungal mycelium spreads throughout the fly and may even reach areas of the brain that control behavior. It manipulates the fly to land, crawl to a high point (a phenomenon known as “summit disease”), and raise its wings—positioning it perfectly for spore dispersal before it dies.
Are you kidding me?
Even the timing of the fly’s death is not random. Most infected flies die just before dusk, typically within a few hours before nightfall. Researchers have found that this window of death follows a kind of circadian rhythm, likely governed by the fungus itself. In other words, the fungus not only controls how the fly behaves, but when it dies, ensuring the spores are released in the cool, humid twilight (ideal conditions for spreading to new hosts).
I know—it’s wild.
The fungus even manipulates flies by making infected females attractive to healthy males. Infected females emit a chemical signal that’s irresistible to males, who attempt to mate with the corpses, infecting themselves in the process.
Nature always has ways of surprising us and filling us with awe, especially when we least expect it. What I thought was just another stretch of trail turned out to be a stage for one of nature’s most bizarre and brilliant survival strategies—one that depends on death.
If you’re curious to dive deeper into the fascinating world of Entomophthora muscae and related topics, here are some sources I found helpful:
This Parasitic Fungus Turns Flies Into Zombie Insects – Smithsonian Magazine
An accessible scientific overview of E. muscae and its behavior.Entomophthora muscae – University of Wisconsin-Madison Extension
A great explainer with photos and background for curious naturalists.Mind Control: How Parasites Manipulate Insect Behavior (Review Paper)
A deeper dive into the mechanisms behind parasite-induced behavior.Circadian Timing of Death in E. muscae-Infected Flies (Research Article)
The original paper discussing “gated” death near dusk.Zombie-Ant Fungi Video – BBC Earth
Different fungus, similar mind-controlling vibes—worth a watch.
