Our hearts often go out to our fuzzy friends in the animal kingdom. But when was the last time you felt sorry for a fruit fly?
Well, you’re about to.
A new study describes a fungus that invades and enslaves these insects, driving them to an end harrowing enough to make Edgar Allan Poe leave the lights on.
As scientists described recently in the journal eLife, the fungus not only drives flies to a gruesome end, but first makes them strike a “death pose” that serves to spread the fungus’ spores far and wide. (See what happens when ants get zombified.)
Lead author Carolyn Elya, now a postdoctoral researcher at Harvard University, was a graduate student at the University of California at Berkeley in 2015 when she noticed the fungus, Entomophthora muscae—Greek for “insect destroyer”—in wild fruit flies that she had baited with a nice, rotting watermelon.
Known since 1855 in house flies, this is the first time this puppet-master fungus has been studied in fruit flies.
The fungus starts by consuming the fly’s hemolymph, the fluid equivalent of blood in invertebrates, and then feeds on the insect’s fat cells. After the free liposuction, the mind control begins. (Related: Nature’s Walking Dead: Mind-Controlling Zombies.)
Before the fly dies, Elya says, the fungus induces the fly “to climb up something nearby” and push out its proboscis, or mouthparts. Then, the fly drools what is likely a fungal secretion onto the surface it’s standing on, a sticky substance that glues the hapless fly to the floor.
The fungus then exerts a kind of mind-control on the fly, causing the fly to lift its wings upright, a position in which the wings “become stuck out from their back at a steep upward angle,” Elya says.
A few hours later, the white fungus can be seen growing out through the bug’s brownish body, making a striped pattern. Spores form at the tips of the fungal fuzz, and then in an amazing display of physics launch from the fly’s body as if shot from a cannon, spreading in search of another fly to infect.
The height of the insect, its raised wings keeping the path clear, and the powerful ejection of the spores—20 miles per hour—means that the spore has the potential to travel farther than, say, if the fly died on the ground, Elya says. All the better to make it to another unlucky host.
Does the fly know what’s happening?
Elya points out a video in the paper of a fly getting its proboscis stuck and start to “sort of freak out,” and claw the surface “like it wants to move.” With a mind-controlling parasite, though, it could just be muscle spasms, she says. It’s easy to guess, hard to know. (Learn more about "mindsucking" parasites in National Geographic.)
How the fungus manipulates the fly’s brain is the next thing Elya and the team will look into. (Related: Meet 5 "Zombie" Parasites That Mind-Control Their Hosts.)
It’s possible, Elya says, that some of the movements are the mechanics of the growing fungus, pushing on muscles and causing the proboscis or wings to stick out.
Only neuro-manipulation, however, can explain “how a fly can orient to a vertical surface,” and “climb up that surface.”
“Neurons aren't supposed to be manipulated by other life forms inside you, just, no,” says Katy Prudic, entomologist at the University of Arizona who wasn’t involved in the paper. She says that being able to study this fungus in fruit flies, long used as a model system by neuroscientists, offers an important advantage.
“One of the exciting things about this paper is that we have all these fine-scale genetic tools to look at what genes are turned on and when” in fruit flies—we don’t have these tools for many other animals.
So the chance to study zombified fruit flies “will give us a deeper insight on how a fungus might be controlling the animal’s behavior,” she says. (See how mind-controlling wasp venom could aid Parkinson's disease research.)
The information could one day help with pest control and disease treatment.
“And how to protect our brains when the zombie apocalypse comes,” Prudic jokes. It's science—and a perfect survival toolkit.