Fly Circus — The Living Simulation

A colorful surreal circus world where six fruit flies live their own lives. They have brains, they get hungry, they find food, they eat, they get startled, they learn places, and they go home. You are a visitor in their world, not the director of it — although you have director's tools.

Made by rbiscutt.

What is built

The world. A striped big top you can walk into, with raked seating and a sawdust ring. Green grounds with trees, bushes, flowers, paths and two ponds. A lobby with a dome and a chandelier, dormitories, a round dining pavilion, a backstage full of scenery, and a cellar under the field reached by a stair through a real opening in the ground. Clouds that are actual 3D geometry and drift on their own. A day/night sky. And below everything, a white void with the inscription floating over it.

The six fruit flies. Each is built from a shared insect plan — a head that is mostly compound eyes, antennae, a thorax, a three-segment abdomen, six legs and two wings that beat — with the character's own design on top: a jester's cap, long ears, a yarn wig, a mask, a crown, or a body assembled from pieces that do not match. They are small: about 0.6 units long, against a 34-unit tent.

Their brains — the important part. Each fly has its own spiking neural network: 198 leaky integrate-and-fire neurons wired into named circuits — five sensory, four drive, three modulatory, two associative, five motor, and a mass of recurrent interneurons. Every fly's wiring is different because every fly has its own seed. Synapses into memory are plastic and reinforcement-gated, so a fly only learns about things that turned out well.

This is a biologically inspired simulation, clearly labelled as such — it is not a real fruit-fly brain. A real Drosophila connectome (164,587 traced neurons) is installable from ZeroMind as the fruitFly package; this world deliberately does not use it, because six full connectomes would not run on the hardware this is built for.

Their behaviour is not a lookup table. Senses go in as currents, motor commands come out as rates, and the creature's temperament scales how much each signal is felt. A fly independently notices food, approaches it, lands, eats, returns to a place it remembers, flees something looming, and keeps to a home range. It navigates the scene's real colliders by raycast and sphere-cast, so it lands on a bleacher because there is a bleacher there.

Playing it

Press play. The flies start on the apron in front of the big top. Walk over and watch them — they are small, so get close. Six food sites are stocked around the grounds when a session starts.

What is not built yet

Being straight about it, because a half-built feature that looks finished is worse than one that is obviously missing:

• The live brain viewer — the 3D rotatable brain with clickable regions. The brain exposes everything it needs (readout() returns every region's rate, position, description and influence), and nothing consumes it yet.
• Speech bubbles. Flies already decide what to say and when, from their own state, and write it to a speaking field. Nothing draws it in the world yet.
• The director sandbox and the game interface — main menu, pause, settings, save/load, audio. None of it exists. There is no music and no sound.
• Adventure environments. The world has one location, not fifty.
• The brain's own input — rotating and clicking the brain display needs an input map; the Luau input surface here exposes almost nothing, so that is a real piece of work rather than a small one.

Known rough edges

• Frame time runs long (~60 ms) in edit mode. The per-fly brain, the raycasts and 60-odd posed joints per creature are the cost; the brain steps are already bounded and obstacle casts throttled, but there is more to do.
• Flies and food are simulated per peer rather than owned by one peer, so two people watching the same world see two different sets of flies.