a field guide · October 2026
Fly-brain videos: what is real?
Since the full wiring of a male fruit fly came out on 3 September 2026, a fly brain has "played" Doom, Mario 64, Minecraft and Beat Saber, doomscrolled a feed and moved a humanoid robot. Some of those videos have been watched tens of millions of times.
Most of them are fun, and most of their makers are honest about what they built, if you read their notes. But the clips travel without the notes. This page gives you five questions to ask any fly-brain video, checks the famous ones against them, and then puts the same questions to us.
01What is actually real underneath
The wiring is real. A connectome is a neuron-by-neuron map of who connects to whom. It is made by slicing or milling the tissue, imaging it with an electron microscope, and tracing every cell with AI and human proofreading. The male fly's map (MaleCNS v1.0, Janelia, Google, MRC LMB and Cambridge) has 166,691 neurons and about 125 million synapses, across the brain, the optic lobes and the nerve cord. The earlier FlyWire map of a female brain has 139,255 neurons.
The brain models are an approximation. The common one (Shiu et al., Nature 2024) treats every neuron as the same simple "leaky integrate-and-fire" unit. Connection strength comes from the number of synapses, and excitation or inhibition from the predicted transmitter. It is surprisingly good: it matched 91% of 164 tested predictions about feeding and grooming circuits. It also leaves a lot out: neuromodulators and moods, learning, the cells' shapes, gap junctions, glia.
A body is the hard part. The brain talks to the body through about 1,100 descending neurons. They go to the nerve cord, where rhythm circuits and premotor cells turn a command like "walk" or "jump" into the timing of motor neurons for six legs, two wings, the neck and the mouth. Fly bodies exist only in simulation (NeuroMechFly, flybody). In every demo we found, including the serious ones, the walking and flying are done by a trained controller, not by the connectome.
02Five questions for any fly-brain video
- What goes in?Which sensory neurons receive the game or the camera, and how? "We sent the pixels to the photoreceptors" is a real answer; "we gave it the screen" is not.
- What comes out, and from which neurons?Which cells are read, and what do they mean in a real fly? A neuron that makes a fly back up being used as "fire" in Doom is a choice by a person, not by the fly.
- What did a person write in between?Hand-written rules, a trained decoder, reinforcement learning, recorded moves played back. Any of these can do the real work while the brain adds noise.
- Is there a control?Does the same thing happen with the wiring scrambled, or with random noise? If yes, the fly's wiring is not what you are watching.
- Whose body, whose code?Is the body a fly's? Can you read the code and the notes? No code and no source means you cannot know.
03The famous ones, checked
From the makers' own code and notes where they exist, and from reporting where they do not. View counts are as reported in the press. None of the makers said anything false that we could find; the gap is between their notes and how the clips were shared.
Doom ("DOOMFLY")
- in
- Game pixels sent to 3,335 brightness and 811 colour photoreceptors; the README calls the pixel positions inferred proxies.
- out
- Left-right difference of DNp20 steers; DNpe017 moves and fires. The README says these are engineered controller assignments, not natural motor functions.
- learning
- Damage drives two dopamine cells and a learning rule. The README reports that the latest version failed its own vision, conditioning and survival tests.
Super Mario 64 ("Fly64")
- in
- Six views around Mario sampled by modelled photoreceptors.
- out
- Walking, turning and escape neurons mapped to forward, steer and jump. The README says plainly that these are rules the makers wrote, with no training, reward or goal.
- critique
- Patrick Mineault: the run is noise-driven, so it looks like playing without adapting to the game.
Minecraft ("NeuroCraft Fly")
- in
- Six game events (something approaching, mobs, touch, attack, food, light) sent to matching sensory groups.
- out
- Readouts chosen by hand select pre-written body programs. No learning.
Beat Saber
- how
- As reported from the maker's comments: motor sequences from recorded data and reinforcement learning on one song; the visual part is still in development.
- critique
- Mineault: overtrained on a single track, barely using vision.
Bad Apple
- what
- Neuron activity beside a simulated fly body flying and grooming. Reportedly built on the Minecraft project's pipeline, so likely its scripted programs. We could not find code or notes.
Doomscrolling ("fly-wirehead")
- how
- The feed scrolls on a timer, so the fly does not choose anything; dopamine cells are driven directly; the body movement is amplified and partly choreographed. Fun, and the code says so.
Reading emotion in speech
- how
- A 499-neuron piece of the wiring as a fixed network, with a trained readout on top.
- result
- Real wiring 16.84%, scrambled wiring 16.88%. Their own control shows the fly's wiring added nothing for this task, and they published it. This is the question 4 test done right.
"A fly brain moving an android"
- what
- The faceless, muscled body looks like Clone Robotics' Protoclone, a separate product shown in 2025. We found no source connecting it to a fly brain.
- closest
- A public project puts the fly brain in a simulated humanoid: a trained policy does the walking, and the brain only picks chase, escape or eat.
- why
- A fly's outputs are commands for six legs and wings. A human-shaped body needs an invented mapping and its own learned controller.
"When the lights go off it freezes, like a fly."
Real flies do not. Sudden darkness gives a short burst of movement, and flies keep walking and exploring in the dark. Freezing is what a fly does to a looming threat, depending on how fast it is walking.
04The serious work, for contrast
Shiu et al. (Nature 2024) tested the brain model against the lab and published where it was right and wrong. NeuroMechFly v2 (Nature Methods 2024) and flybody (Nature 2025) built physical fly bodies; their walking and flight come from trained controllers. FlyGM (arXiv 2026) runs the wiring as a fixed network inside flybody with a trained encoder and decoder. Eon Systems (March 2026) joined the brain model, a vision model and NeuroMechFly; a critic noted that only a few descending neurons were read and fed to pre-trained walking controllers. None of these say a fly was uploaded. All of them tell you exactly what they did.
05The same five questions, put to us
One model of a male fruit fly's whole nervous system, running live
- model
- The Shiu et al. leaky integrate-and-fire model on the MaleCNS v1.0 wiring, 165,122 neurons in our build. With all its limits above.
- in
- Poisson spikes into named sensory groups: odorant receptor neurons for smells, taste neurons on the labellum, looming detectors LC4 and LPLC2 for a growing shadow, and so on.
- out
- We read the descending neurons (the giant fibre for escape, MDN for backing up, grooming neurons), the motor neurons for the mouth and wings, and the mushroom body's output neurons.
- written by us
- The thresholds and their order that turn those readings into one word (flee, sing, approach, avoid, groom, walk, rest); the strength of each stimulus; how a lesson changes the mushroom body. The fly's drawn body is an illustration of that word, not a simulated body.
- control
- Not yet. We report seed-to-seed spread, and we publish where the model fails, but we have not run scrambled wiring against every behaviour. We should.
- in our games
- Flappy Fly takes its escape delays from 312 runs measured beforehand; the brain does not run while you play, and the jump height is game design.
If you see a claim of ours that these five questions do not support, tell us and we will fix it or take it down.
06Sources
- MaleCNS v1.0 release, Janelia: male-cns.janelia.org/release · Google Research: a connectomics milestone
- FlyWire whole-brain connectome, Nature 2024: PMC11446842
- Shiu et al., a Drosophila computational brain model, Nature 2024: PMC11446845
- Descending neurons of the fly: PMC4738306
- NeuroMechFly v2: bioRxiv 2023.09.18.556649 · flybody, Nature 2025: PMC12310536 · FlyGM: arXiv 2602.17997
- DOOMFLY: github.com/nftechie/doomfly · Fly64: github.com/ornata/fly · NeuroCraft Fly: github.com/evnsnclr/neurocraft-fly-public · fly-wirehead: github.com/mattyhempstead/fly-wirehead · humanoid project: neomorrison/malecns-test
- Reporting: 404 Media · Gizmodo · Dexerto · Know Your Meme · Oruk Labs summary
- Critiques: Patrick Mineault, Are flies playing Beat Saber? · Ariel Zeleznikow-Johnston, No, we haven't uploaded a fly yet · The Register on Eon Systems: digital fly walks
- Clone Robotics Protoclone: New Atlas
- Flies in sudden darkness: PMC10135638 · walking in the dark: PMID 20581279 · freezing to looming, Zacarias et al. 2018: Nat Commun 9
An independent project, not affiliated with Janelia, Google, Cambridge or any maker named here.