HouseFly — a real fly brain, running your house

Why this was rewritten

HouseFly v1 described itself as a “leaky reservoir inspired by fruit-fly motifs”. That framing was doing a lot of work. The brain was a 256-unit reservoir whose recurrent weights, input projections and readouts were all drawn from rng.gauss — and none of which ever changed.

So every motor channel was a fixed random projection of a random projection of your sensors: statistically, a smoothed Gaussian hovering near 0.5. Nothing the fly did depended on anything. Every behaviour you could actually observe — the mode classifier, hunger, phototaxis — was a hand-written if sitting beside the reservoir rather than emerging from it. You could have deleted the reservoir without changing what the integration appeared to do.

It also named the connectome in its docstring and then explicitly declined to use it. And it fired a service call at every configured output every ten seconds with a value that was noise — cover was a supported output domain, so the documented configuration surface included your garage door.

The question was never how to improve the reservoir. It was why there is one.

Give each circuit the input it actually carries

The replacement is not a bigger network. It is a set of circuits that have a known function, each receiving the kind of signal it receives in the animal.

Circuit	What it does in the fly	What it gets from your house
EPG / PEN / PEG / Δ7	Ring attractor holding heading	Integrates the fly's own turns into a compass
ER ring neurons	Visual bearing into the ellipsoid body	Bearing to every card on your dashboard
PFL3	Compares heading to goal, commands a turn	Steering (see the caveat below)
KC → MBON	Associative memory, real plasticity	Learns which parts of the house are good
PAM / PPL1	Reward and punishment teaching signals	Feeding it, and swatting at it
LPLC2 → DNp09/10	Looming detection → escape	Motion sensors firing; your cursor
Projection neurons	Odour identity	The state of your house, as a smell
s-LNv / LNd / DN1	Circadian morning + evening oscillators	Real local time

There is no rule anywhere that says be active at dawn. The morning cells are driven by morning, the evening cells by evening, and arousal is read off their firing rate. The fly is crepuscular because the circuit is.

The ring attractor is in the wiring, not in the code

This is the part worth showing people. Nobody wrote a ring attractor. The connectome contains one.

Take the effective EPG → Δ7 → EPG coupling — using only measured synapse counts and the protocerebral bridge glomerulus labels — and bin it by heading offset:

0° 89 ▉

45° 181 ▉▉▉

90° 919 ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉

135° 1791 ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉

180° 2025 ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ ← peak

225° 1827 ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉

270° 921 ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉

315° 208 ▉▉▉

Δ7 is inhibitory, so this is local excitation with long-range inhibition — a Mexican hat, 23:1. That is exactly, and only, what a ring attractor needs. Run python3 tools/build_connectome.py and it prints this from the raw data.

The data caught a mistake before the simulation did

The first version of this gave both halves of the protocerebral bridge the same angular order. That produced a much weaker 2.7:1 profile, and a compass that held a heading perfectly well but would only ever turn one way.

The real bridge is a mirror-symmetric double map. Correcting it sharpened the signature from 2.7:1 to 23:1. The connectome said the anatomy was wrong before a single neuron was simulated.

Which way does a turn push the bump? Measure it.

You do not have to assume. It is readable straight out of the synapse counts:

EPG → LEFT  PEN1 → EPG loop shift:  +12.5°
EPG → RIGHT PEN1 → EPG loop shift:  −11.5°
EPG → LEFT  PEG   → EPG loop shift:   −5.6°
EPG → RIGHT PEG   → EPG loop shift:   +0.9°

PEN loops shift the bump in opposite directions per hemisphere. PEG loops do not shift it at all. That is the textbook split between the loop that moves the bump and the loop that holds it — and it fell out of the data.

It has a memory, and the memory is synapses

Learning in Drosophila happens at Kenyon cell → MBON synapses. A Kenyon cell active at the same moment as a dopaminergic neuron in that MBON's compartment gets depressed. That is the whole rule. It is anti-Hebbian, and it is why a fly stops approaching things that turned out to be bad.

HouseFly implements exactly that, on 20,391 real KC→MBON connections. Each MBON's compartment valence is derived from which dopaminergic class dominates its input, rather than hard-coded. Those gains are what persists across restarts — the fly does not forget your house when Home Assistant updates.

What the connectome does not contain

Two things were expected to fall out of the wiring and did not. Both are worth stating plainly, because “we tried to derive it and could not” is a result.

The map of your house

The plan was to read the landmark-bearing → heading mapping off the ER → EPG connectivity. It isn't there: that projection is near-uniform, about 7% modulation depth, with no consistent phase.

This is not a gap in the data. In the real animal that map is learned, in plastic ER→EPG synapses (Fisher et al. 2019; Kim et al. 2019). A naive fly does not have one. So HouseFly doesn't fake it — the compass integrates the fly's own turns, exactly as a real one does in the dark, and it drifts when it cannot see.

PFL3's steering computation

In the animal, PFL3's left-right imbalance is the turn command, because each cell's fan-shaped-body arbor sits about a quarter turn from its bridge arbor, in opposite directions per hemisphere.

We tried it both ways — feeding the goal into the fan-shaped body and letting the connectome do the rest, and imposing the quarter-turn offset explicitly. Neither gave reliable goal-following: the correlation between turn command and the sine of the heading error ranged from +0.03 to −0.54 depending on the trajectory, and the closed loop never converged. That offset is where the arbors physically sit, and synapse counts between cell types do not carry it.

So the goal-seeking controller lives in coordinator.py — four lines of proportional control, labelled as a controller. The fly holds a heading using a connectome-derived ring attractor, which is real, and chooses which heading to hold using arithmetic, which is not. Keeping those visibly separate matters more than having one more thing to claim.

What a real house exposed

The fake ten-room testbed was generated, tidy and metric. Pointed at a live installation instead — Swedish, 30 lights, Bluetooth room-presence sensors, a power meter and an electricity price — the sensory front end turned out to be destroying most of its input before a single neuron saw it.

Every word became the same number

Any state that wasn't numeric returned a constant 0.35. So Allrum, Loft and Kitchen all arrived as the same smell, and the mushroom body could not learn that one room differed from another. The information was gone before it reached a neuron.

Words now pick a glomerulus rather than a magnitude — which is how odour identity actually works: it is carried by which neurons respond, not how hard one does. With 131 glomeruli some states inevitably collide, as they do in a real fly with about 50 for an unbounded number of odours. That is resolved where the animal resolves it: two colliding inputs still produce clearly different Kenyon cell codes — 67 and 39 cells active with 12% overlap — because the projection-neuron-to-Kenyon-cell divergence in the connectome pulls them apart.

One scale cannot serve degrees, watts and currency

tanh(value / 60) put seven temperatures spanning 11–25 °C into a 0.2-wide band, pinned a 2,840 W power sensor flat at 1.0, and turned an electricity price of 0.43 into 0.007. Two of those channels were constants and the third had no resolution left.

Each channel now learns its own range and reports where the current value sits inside it — receptor neurons adapt their gain to the stimulus range they actually receive, which is why you can see indoors and outdoors. It costs two floats per entity and they persist across restarts.

Three smaller ones, all of a kind

abs(value) meant −15 °C and +15 °C were identical readings. On a Swedish install, that sign is the signal.
sun.sun reports above_horizon, which didn't parse as a number — so the sun was a constant.
Dead inputs were silently read as zero. On the install tested, four of nine configured inputs were unknown and nothing said so. A sensor stuck on unknown is not a smell of nothing; it is no smell at all.

Honest limits

This is a real model of real circuits, and it is still a model.

4,724 neurons of roughly 25,000 in the central brain, and no body, no muscles, no proprioception. Most of the input these cells really receive comes from neurons that aren't in the subnetwork, which is why there is a tonic drive term standing in for the rest of the brain. That term is an assumption.
A rate model, not spikes. One leaky rate unit per neuron, following Shiu et al. 2024. No dendrites, no delays, no channel dynamics.
Synaptic sign comes from predicted transmitter. Mostly reliable — but FlyWire's classifier returns acetylcholine for most ring neurons, which is wrong; they are GABAergic. Where the literature is settled it overrides the prediction, and every override is listed in the build tool.
Two circuits needed a static gain constant. The fan-shaped body and the Kenyon cells are large and almost entirely excitatory with no matching inhibitory population inside the modelled subnetwork, so without it they flood.
Two brains, spliced. Connectivity is hemibrain; positions and transmitters are FlyWire — a different fly. Joined by cell type, which is standard practice and still an approximation.

It is not conscious, it is not an agent, it does not understand your house, and it is not a scientific instrument. It is a small animal's wiring diagram with your sensors plugged into it.

Everything above is checkable

python3 tools/validate.py runs the shipped brain and checks all twenty-six claims, printing the numbers — including the marginal ones. CI runs it on every push, alongside HACS's own validation action and Home Assistant's hassfest.

a bump forms                               peak 0.223, trough 0.000     PASS
it holds still with no self-motion         0 deg of drift               PASS
turning rotates the bump, right direction  correlation +0.99            PASS
punishment depresses KC→MBON synapses      20,391 plastic synapses      PASS
looming raises descending drive            0.0000 → 0.2452              PASS
  ...and the escape is transient           fell back to 0.0000          PASS
PFL3 cells are not all at the same rate    spread 0.0038                PASS
arousal  03:00 0.17  06:00 1.00  12:00 0.08  18:45 1.00  23:00 0.10     PASS

Installing it

HouseFly is a HACS custom repository. In Home Assistant:

HACS → ⋮ → Custom repositories
Repository https://github.com/Vortitron/HouseFly, type Integration
Install HouseFly, then restart Home Assistant
Settings → Devices & Services → Add Integration → HouseFly

Both Lovelace cards register themselves — no resource setup needed:

# Lets the fly out onto this dashboard. Draws nothing itself: it reports
# where your cards are and paints the fly over the top of them.
- type: custom:housefly-overlay
  show_debug: true

# The connectome, with live activity in it.
- type: custom:housefly-brain-card

Somewhere safe to try it

The repository ships a testbed/ — a throwaway Home Assistant with a fake ten-room house: 24 lights, 23 switches, 30 drifting sensors, 15 motion detectors, all template helpers with nothing behind them, plus six entities that exist purely so you can watch the safety layer refuse them.

git clone https://github.com/Vortitron/HouseFly
cd HouseFly/testbed && ./up.sh     # http://localhost:8124

Or skip the setup entirely: Vome hosts Home Assistant instances you can create in a few seconds, which is where the live demo of this runs.

Safety

A fly with write access to your house is a bad idea unless the boundaries are real ones.

Actuation is off by default. A fresh install watches and walks; it touches nothing until you deliberately turn it on.
Never, regardless of configuration: lock, alarm_control_panel, cover, climate, water_heater, humidifier, valve, vacuum, lawn_mower, script, automation, scene.
Refused by name even in an allowed domain: anything containing boiler, freezer, pump, oven, server, alarm, garage, charger, and about twenty more.
It has to land on something to touch it. Actuation is triggered by the fly settling on a card, not by a timer — a few interactions an hour, not thousands.
Hourly budget, per-entity cooldown, a deadband so a jittering brain cannot produce a call storm, and optional quiet hours.

Start it on a spare lamp.

Data and credit

Both datasets are CC-BY 4.0, and both are fetched at build time rather than vendored.

Connectivity, cell types, columnar labels — Janelia hemibrain v1.2. Scheffer, Xu, Januszewski, Lu, Takemura, Hayworth et al. (2020), A connectome and analysis of the adult Drosophila central brain, eLife 9:e57443.
Soma positions, transmitter predictions — FlyWire FAFB. Schlegel, Yin, Bates, Dorkenwald, Eichler, Brooks et al. (2024), Whole-brain annotation and multi-connectome cell typing of Drosophila, Nature 634:139–152.
Modelling approach after Shiu, Sterne, Spiller, Franconville, Sandoval, Zhou et al. (2024), A leaky integrate-and-fire computational model based on the connectome of the entire adult Drosophila brain, Nature 634:210–219.

The flies did the hard part.