In our series, A Scientist Responds, we’re dredging up the great and terrible science fiction flicks of days past—and we’re making scientists watch them. Today’s movie: David Cronenberg’s 1986 remake of the B-movie screamer, The Fly. The scientist: Throb editor and resident biologist, Diane Kelly.

The Movie: The Fly

The Fly is a story about the dangers of sloppy lab techniques, the perils of poor communication, and, oh, also Jeff Goldblum’s terrifying transformation into some sort of human-fly hybrid.


The story begins when eccentric inventor Seth Brundle (Jeff Goldblum) brings science journalist Veronica Quaife (Geena Davis) to his warehouse apartment cum laboratory to show off the teleportation device he’s been working on. Naturally, she wants to publish an article about the device—who wouldn’t—but he begs her to wait, offering her exclusive access as he attempts to make the machine capable of teleporting living things. They soon become lovers, because, Hollywood. But when Brundle finally gets the machine to work on living tissue, Quaife’s editor and former lover (John Getz) threatens to break the story. When Quaife heads to the office to tell him off, Brundle gets the wrong idea. In an alcohol-and-jealousy-fueled haze, he runs himself through the teleporter without noticing that a housefly is in there with him. Everything pretty much goes to shit from there, as Brundle slowly turns into a human-fly-monster-thing and loses his mind.

The Science

Okay, let’s just get this out of the way: There is a teleportation device and it is basically just a magic box. That’s it. There is no science to it (as there shouldn’t be). Many of the other ideas that drive the story, though, fall squarely in the realm of biology, or at least, something close to it. So let’s see how some of those square up with real life.


Premise #1: Brundle’s first successful test subject had no ill effects because it was the only living thing in the telepod at the time.

Um, no. That lab is pretty much the polar opposite of a cleanroom, and Brundle seems to be pretty shaky on the details of sterile technique. He has his kitchen about 3 feet from the “landing” telepod, for god’s sake!


That means that when he teleported his baboon test subject (and while I’m complaining about his lab technique: WTF, a baboon? If it has to be a mammal, hasn’t this guy heard of rats?) a whole ecosystem of microorganisms went along for the ride.

Not only would there be plenty of living things in any dust that settled inside the telepod—one recent survey of household dust across the United States found an average of 4700 types of bacteria and 1400 types of fungus floating around people’s homes—there are also all the microbes that live on or inside the baboon.

You could assume that the device only rebuilt the baboon and killed all the microbes in the process. But if that was the case, the baboon would have come out of the pod without the gut bacteria that help it make vitamins and digest food. The effects wouldn’t be immediate, but even Brundle wouldn’t be able to ignore that monkey’s gastrointestinal distress once it set in.


Verdict: Clearly false, given the laboratory conditions we’re shown.

Premise #2: Brundle develops fly-like traits because the machine integrates fly DNA into his genome.


Let’s assume for argument’s sake that those fly genes aren’t inserted willy-nilly into Brundle’s chromosomes, disrupting genes for core physiological functions in their wake. (Because breaking genes that help make critical proteins like neurotransmitters or metabolic enzymes would make this a very short movie.) So the machine has carefully integrated the fly genes into the chromosomes inside all of Brundle’s cells in a way that could let them get read and used.

Here’s the thing: 60% of the human genome is already pretty much identical to a fly’s.

Taking those genes out of a fly and putting them inside a human just means that the human gets another copy of a bunch of genes he already has inside his cells. A fly gene doesn’t have any magic ‘fly-ness” that makes it do “fly” stuff—like every other gene, it’s the code for a protein (or a strip of regulatory RNA, but let’s try to keep things simple here). If it happens to be a protein that humans make too, in the context of a human cell it’s going to work like a human protein.


Of course, flies make plenty of proteins that humans don’t. They have enzymes that let them assemble sugars into a chitin exoskeleton. They have specialized sex pheromones. One survey of the housefly genome from 2014 found genes for unique immune and detoxification proteins that might help them resist infections from the human pathogens they carry. Inserting these genes into human cells would make it possible for the human to make proteins that had evolved in the fly. But it still won’t turn the cells into fly cells–the fly genes would get expressed in the context of human biology.

Plus, just being inside a human cell isn’t enough to turn the fly genes on: most of the genes on any chromosome are coiled up in a way that keeps them from being read by the cell. I’ll spare you the technical details–suffice it to say that although every cell in the body contains the entire genome, each cell also regulates which genes it turns on and leaves the rest of them effectively turned off. That’s how the cells in your body manage having different jobs: skin cells make proteins specific to skin, neurons make proteins specific to neurons, and so forth.

So while Brundle’s cells have gotten a sudden infusion of unique fly genes, those genes aren’t going to get turned on unless they’re in a cell with the right internal environment to unpack and read them. I’m not sure how you’d even predict which genes would get read by any particular type of cell, but I’m certain that you’re far more likely to see random changes in tissues scattered around his still-human body than any organized shift to fly-like physiology.


If he’s very very lucky, he might become immune to typhoid fever, tuberculosis, and dysentery. Or maybe parts of his intestinal lining will start growing flat patches of chitin. Or both. But an overarching and organized shift in gene expression? No.

Verdict: It’s a mixed bag—though the reality could be much uglier, and much less organized, than the transformation we see on screen.


Premise #3: The weird and disgusting stuff that happens to Brundle over the course of his transformation are based on things that are actually true about flies.

Some of this is actually pretty close. The first changes we see are Brundle’s new sensory hairs, which appear on his back at the same time that he gets faster reflexes, a supernatural increase in strength, and an enormous sexual appetite. Later changes affect the way he eats and moves.


Flies certainly do have excellent reflexes – anyone who’s tried to swat one can attest to that. Those tiny hairs that cover their bodies sense air flow, and let flies react to changes in air currents long before the big object that’s pushing the air reaches their bodies. As Brundle’s transformation progresses, we learn that he’s vomiting up acid to dissolve his food and sucking up the soupy mess afterwards. And yes, flies do eat that way (though they’re spitting up enzymes rather than raw acid). In fact, their spongelike mouthparts make it impossible for them to eat any other way.

As for the non-stop sex, well, male flies are definitely horny beasts. Once they’re sexually mature they’ll try to mate with anything that’s even vaguely fly-shaped: female flies, other males, pupae, dead flies. They also release a mating pheromone from their genitals that attracts females. I think I’m glad the screenwriters didn’t try to incorporate that particular natural history fact into the script.


But the science isn’t all good. Strength, for instance, isn’t really a fly’s strong suit. Flies can carry about 1.6 times their body weight: translated to human terms it’d mean that the 185-lb Brundle would be able to lift 278 lbs. Impressive, to be sure, but hardly superhuman: the record holders for Olympic weightlifting in Brundle’s weight class lifted considerably more than that: 388 lbs with the snatch and 462 lbs in the clean-and-jerk. So that scene with Brundle managing to literally break someone’s arm in half while arm wrestling is probably not happening.

Also, that mysterious secretion coming out of Brundle’s hand during the scene? No. Flies also don’t ooze acid from their feet.

Verdict: Not perfect, but overall, an effective use of real fly natural history to evoke real horror.


Premise 4: Having moved through some creepy interim stages, Brundle suddenly transforms completely into a giant fly-thing.

At the climax of the film, Brundle’s human body falls away to reveal a flylike monster inside. This isn’t just viscerally disgusting, it’s a marvelous adaptation of real fly biology.


Like butterflies, flies are insects with complete metamorphosis, going from larva to pupa to adult over the course of their lives. Maggots (or caterpillars) don’t simply grow into flies (or butterflies). Inside a pupa, the insect is dissolving parts of its larval body and using it to fuel the growth of its adult form. Which suggests that as we watch Brundle deteriorate over the course of the movie, we’re really watching a perverse form of pupation, as the Brundlefly dissolves its larval human body to build its appalling new form.

Verdict: Sure, why not! If you somehow manage to avoid all the other issues of genetics, microbes, and the magic box used to accomplish everything, this one actually has some scientific chops to it.


The Judgement

Completely implausible, of course. Cronenberg’s decision to transform man into fly-thing gradually over the course of the film makes the remake a far better movie than the 1958 original. But in the end, it’s just as much rubber science as the original’s straight up swap of head and arm between human and fly.

[Barbaran et al 2015 | Tung et al 2015 | Gilbert 2013 | Scott et al. 2014 | Murvosh 1964 | Schlein and Galun 1984 | Lehmann and Dickinson 1998]


Fly with sensory hairs visible by Martin Cooper via Flickr | CC BY 2.0; Fly mouthparts by Josef Reischig via Wikimedia | CC BY-SA 3.0


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