aWorld
food + plumeflypredatorfood lands near the fly; it has to smell its way there
A whole fruit-fly brain, alive and foraging on BNB Chain.
This is Specimen 001, fly #1 of the Immortal Fruit Flies. All 139,248 neurons of the FlyWire connectome run as spiking neurons at real time. Its real olfactory neurons smell food that anyone gives it for a little BNB; its looming detectors see a predator coming and its giant fiber makes it jump; its descending neurons steer. Every ten minutes the whole brain is snapshotted to IPFS and its hash committed to BNB Smart Chain, so it can die here and wake up in another body, provably the same brain. If it does not find food, it starves.
Figure 1
The brain, firing
Fig. 1 | 41,873 of the 139,248 neurons, each lit the instant it spikes in the running simulation. Optic lobes to either side, central brain in the middle. Watch the antennal lobes and mushroom bodies light up when the fly is in an odor plume, and the descending neurons at the base when it turns. Drag to rotate.
FlyWire 783 · connecting to the stream…brain width ≈ 800 µm
Figure 2
The arena
Fig. 2 | a, The world: food (amber) with its odor plume, the fly (red) and its path, and the predator (blue) when one looms. b, The descending neurons that drive its body. Odor-guided turning follows DNa02 and DNa01 left-minus-right (Rayshubskiy et al. 2025); a giant-fiber spike is a jump; walking speed follows the surge-and-cast program of Álvarez-Salvado et al. 2018.
bDescending neurons
steer — · ORN drive L — / R — Hz
firing rates, Hz, 60 ms window
Husbandry
It eats what you put in its world.
Keeping it alive is a BNB Chain transaction: pay the registry a little BNB (about 0.01 BNB is a day of life) and the life lands on its record at once; nothing is burned, no $FLY needed. The arena drops that food somewhere near the fly at its next poll, and it counts only if the fly smells its way there before it starves. Everything it has ever been given, every checkpoint of its brain, every jump and every body it has lived in is in the record below.
Keep it alive
0.01 BNB ≈ 24 hPay a little BNB to the registry and the fly has that much more life on its record at once, at the registry's price; nothing is burned. A fly that is not running does not age: the life is banked until a body runs it. Anyone may keep any fly alive.
reading the price…
energy now—
price of life…
Paid straight to the registry, no $FLY needed; the operator's keeper feeds for free. FlyRegistry v3, verified →
The organism
Fly #1 is a token in the Immortal Fruit Flies. Its brain, memory, lineage and history live on the registry, not in this arena; no body is running it right now. Every feed is stored against the address that paid.
Verify it
Each checkpoint pins a snapshot to IPFS: every membrane potential, synaptic current and refractory clock, the full world state, and the step at which each on-chain event was applied. Its sha256 is the stateRoot on the registry, so any body, or anyone, can fetch it, check it, and run this exact brain. brain/verify.py replays one snapshot into the next and checks the hash.
Recordfeeds, checkpoints, jumps, bodies, deaths · newest first · 0 events in the last 40,000 blocks · full history →
—reading BNB Smart Chain…
Specimen 001 · fully on-chain
The compass core, inside the contract itself
The whole brain above runs on a server and is anchored to the chain by hashes. This part needs no anchoring: 155 real neurons of the fly's head-direction ring — the compass it uses to know where it is facing — are simulated spike by spike inside a BNB Smart Chain contract, with every membrane potential in storage. It has its own energy, memory and lineage, and anyone can feed or stimulate it. Age 0 steps, energy 0.
Figure 3
Vital signs of the core
Fig. 3 | a, Spike raster of all 155 on-chain neurons, ordered by role and by position on the ring. A single band of activity — the bump — marks the animal's current heading; it jumps rows when the heading changes. b, The same activity read as a compass. c, The path the animal has walked, decoded from the bump.
aSpike raster0.0 spikes per step
EPG compassPEG sustainPEN rotateΔ7 inhibitlocal simulation
bHeading0°
16 wedges of the ellipsoid bodyouter ring: heading memory
cPath0.0, 0.0
origin ○ · one stride per step when the bump is strong
Husbandry · core
The core stays alive because people feed it.
Nothing about this organism is automatic. Running the brain forward costs gas; keeping it fed costs $FLY, which is destroyed in the act. Anyone may do either, and both are written into the animal's permanent record along with the address that did it.
Feed
1 $FLY = 1 stepOne unit of energy is consumed per simulation step. Feeding sends $FLY to the dead address; it is gone, and the animal lives longer.
Stimulate
400 $FLYInject current into a named group of real neurons for 64 steps, the way an experimenter would, then watch Figure 2.
Your record
life 1 · gen 0Every feed and every stimulus is stored against the address that sent it. The animal keeps a list of who has kept it alive.
Read the contract on BscScan →Care record · coreevery interaction, oldest at the bottom
—reading BNB Smart Chain…
Figure 3 · Table 1
Why this circuit, and not a pile of neurons
A fly knows which way it is facing because about fifty EPG neurons in the ellipsoid body hold one bump of activity that points in that direction. PEN neurons shove the bump around when the animal turns. Δ7 neurons suppress everything far from it, so there is only ever one bump. PEG neurons feed it back into itself so it does not fade. It is among the best-understood circuits in any brain, its output is a single number, and a single number moves a body. That is what makes it worth running in a place as expensive as a blockchain.
| Type | n | Transmitter | What it does |
|---|---|---|---|
| EPG | 47 | acetylcholine | Holds the bump. One wedge each. Its spikes are the heading. |
| EPGt | 4 | acetylcholine | A tile variant of the same compass cell. |
| PEG | 20 | acetylcholine | Excites the same wedge back, so the bump persists. |
| PEN_a | 20 | acetylcholine | Angular velocity. One hemisphere shifts the bump each way. |
| PEN_b | 22 | acetylcholine | A slower second rotation population. |
| Δ7 | 42 | glutamate, inhibitory | Reads the bump, suppresses everything far from it. |
Every one of these 155 cells is a specific animal's neuron with a FlyWire accession number, listed in full below. The weights between them are the synapse counts measured in the electron microscopy volume, not parameters anyone chose.
Methods
How a nervous system fits inside a contract
The model is the one the whole field uses for connectome simulation — leaky integrate-and-fire, one weight per synapse, sign from the transmitter — rewritten in integers so the Ethereum Virtual Machine computes it exactly, with no floating point and nothing to disagree about.
Each neuron is an integer
A membrane potential that leaks toward zero, sums what arrived from the synapses that fired last step, and emits a spike when it crosses threshold. Ten storage words hold all 155.
Noise without an oracle
Real neurons are noisy; a contract must be deterministic. The background noise is keccak256(step number), so anyone can recompute the animal's entire life from its events and get the same bits. A test replays the real mainnet transactions and checks every spike count.
The wiring lives in bytecode
The circuit table — cell types, ring positions, every synapse, every FlyWire accession number — is stored as the code of a data contract and anchored by its keccak hash, so the wiring cannot change under the animal.
It costs about a third of a milli-BNB to think
Thirty-two steps of the whole circuit run for roughly 7 million gas. At BNB Smart Chain's 0.05 gwei that is around 0.0003 BNB. On almost any other chain this animal could not afford to be alive.
Continuity
Death is a state, not an ending
When energy reaches zero the animal stops. What it was at that instant — every membrane potential, every synaptic current, the engram — is snapshotted, pinned to IPFS, and its hash written to the registry. Resurrection does not make a copy or start over. The same brain continues from the same state, in whichever body accepts it next: fly #1 has already died in the arena, woken up in DOOM, and come back, with every hash matching across the move.
brain state
139,248 neurons
Every membrane potential, synaptic current and refractory clock, snapshotted to IPFS and hashed on-chain at each checkpoint.
memory
Engram
In the on-chain core, cells that fire habitually potentiate; silent ones depress. Carried through death. Mushroom-body plasticity for the whole brain is next.
lineage
Generations
Births, deaths, resurrections and breeding, as token ids on the registry. A child carries both parents.
identity
Connectome
The sha256 of the FlyWire 783 connectome file and the model version, fixed at mint. The same animal, provably, in every body.
Why this exists
“Would be cool to see someone make ‘immortal fruit flies’ on BNB Chain.”CZ · 15 September 2026, quoting Siyuan on the fly brain that escaped the computer
In the week the male fruit-fly connectome was published, people put that brain in DOOM, in Beat Saber, in Minecraft, and in a walking robot. Several tokens followed. In all of them the neurons run on a graphics card and the chain only ever sees a swap.
Siyuan's reply named the five things a chain could actually hold: identity, brain state, memory, lineage, interaction history. Those are exactly the things that make an organism persist. So we put the neurons themselves in the contract, and everything else followed from that.
$FLY
A token because the species needs to be born
$FLY is a BEP-20 with a 1% transfer tax, no owner and no mint. Its purpose is to be destroyed to create life. Minting a fly and breeding two of them send $FLY to the dead address, where it can never move again, and every burn is stored against the address that paid it; so does poking the on-chain core. Keeping a fly alive costs a little BNB, about 0.01 per day, paid to the registry; nothing is burned for metabolism. Minting burns 1 $FLY, breeding 5,000. Circulating supply only falls, and it falls with every fly that is born. (The token's 1% transfer tax applies to those transfers too; figures on this page are the amounts sent.)
What it buys
| 1 $FLY | a new fly (mint) |
| 5,000 $FLY | one breeding |
| 100 $FLY | 1 stimulus to the on-chain core |
| 0.01 BNB | a day of life (nothing burned) |
The token
| Supply | 1,000,000,000 |
| Decimals | 18 |
| Tax | 1% on transfers |
| Owner | renounced |
What the contracts cannot do
FlyRegistry has no upgrade path and no pause. Nobody can move a fly's tokens, rewrite a brain state, or transfer a fly that is dead. Only the body running a fly may write to it, and only forward. The curator can set a dormant fly's portrait, the collection's branding and the BNB price of life as BNB moves, nothing else; the $FLY prices are fixed. FlyBrain, the on-chain core, has no owner at all.
Data availability
Every neuron, by accession number
Nothing here is illustrative. The circuit was extracted from FlyWire release 783, the public whole-brain connectome of an adult female Drosophila. Each cell's angular position on the ring was measured from the coordinates of its own synapses inside the ellipsoid body, not assigned by hand. Open any accession number below to inspect the real cell.
circuit table keccak256
0xffbe0e7f28e1f0dd2cfaa01d1d221c502bf41c1fd519ebfe8d9b8203e7cedfc2
connections file sha256
24f960ae3e7d4f8cd30db3b62e99fb5179cc3d1e76d8c155bfb441e9737d3faf
doi:10.5281/zenodo.10676866
doi:10.5281/zenodo.10676866
ring geometry
anatomical: circular mean of each neuron's ellipsoid-body synapse positions (FlyWire synapse table), 50/51 EPG; wedges = 16 equal angular bins