Figure 1: Slime mold (Physarum polycephalum) spreading a yellow fan-shaped protoplasmic streaming towards its oatmeal food source on damp filter paper (*Image is for illustrative purposes only)
[!NOTE] *All microorganism images used in this article are 3D CG illustrations.
🎯 Quick Summary & FAQ (Key Takeaways)
Before we dive into the detailed guide, here are quick answers to the most common questions.
Q. Where can I get slime mold (Physarum polycephalum)? A. Sclerotium sheets (dried dormant state) are sold cheaply online (on Amazon or specialized scientific supply shops) for educational use. You can also collect wild yellow plasmodia by carefully searching under damp decaying wood and fallen leaves in forests, especially during the rainy season.
Q. How much food should I feed them? A. Place “1 or 2 flakes” of oatmeal slightly ahead of the growing tips of the slime mold. Although slime mold is a voracious eater, giving too much food at once will cause the oatmeal to mold or decay due to bacteria, which can kill the slime mold. The golden rule for long-term maintenance is: “only add more food once the previous portion is consumed.”
🔬 1. Brainless Intelligence? The Fascination of Physarum polycephalum
Despite lacking a brain, neurons, or sensory organs, it can solve mazes via the shortest path and spontaneously recreate efficient paths that resemble the Tokyo rail network. This mysterious single-celled organism showcasing such amazing “intelligence” is Physarum polycephalum (commonly known as yellow slime mold).
Taxonomically, it is not a fungus (like mushrooms or molds), plant, or animal, but belongs to the myxomycetes (plasmodial slime molds), which are closely related to amoebas. During its growth phase, it spreads as a single, giant, multinucleated cell called a “plasmodium,” crawling around while pulsating its yellow veins like a living creature.
Its dynamic movements and beautiful geometric patterns make it the perfect subject to grow in a tiny petri dish on your desk.
🧫 2. Tools and Environment Required for Oatmeal Culturing
Culturing slime mold is incredibly simple and doesn’t even require agar powder to gel the medium.
- Slime mold starter (sclerotium sheet, etc.): The material to start the culture.
- Culture vessel (petri dish): A shallow plastic or glass dish with a lid for easy observation.
- Filter paper (or paper towel): Placed at the bottom of the dish to retain moisture.
- Food (oatmeal): Plain, unflavored rolled oats are best.
- Base water: Dechlorinated tap water or purified water.
- Light-blocking box or aluminum foil: Slime mold dislikes strong light and moves away from it (negative phototaxis), so it should be kept in the dark.
📋 3. Step-by-Step: Breaking Dormancy and Daily Maintenance
Here are the steps to wake up the slime mold from its dried, dormant “sclerotium” state into an active “plasmodium” state and keep it healthy.
[Sclerotium (Dried Dormancy)]
│
▼ (Add drops of water)
[Plasmodial Awakening] (A few hours to half a day)
│
▼ (Feed oatmeal)
[Fan-like Expansion & Growth] (Moves several cm in 24 hours)
│
▼ (Daily maintenance & mold removal)
[Huge Colony Formation] (Fills the entire petri dish)
1. Setting Up the Moist Environment
Place a piece of filter paper (or paper towel cut into a circle) at the bottom of a clean petri dish. Drip a few drops of dechlorinated water to make the paper damp. If there is standing water, tilt the dish and absorb the excess with a paper towel (excessive wetness can suffocate the slime mold).
2. Placing and Awakening the Sclerotium
Use tweezers to place the small piece of paper containing the dried sclerotium in the center of the damp filter paper. Add a single drop of water directly onto the sclerotium. Cover the dish, wrap it in aluminum foil, and leave it in a dark place (room temperature 20–25°C). The dried, brown sclerotium will emerge as a yellow, amoeba-like plasmodium in 3 to 4 hours at the earliest, or within half a day at the latest.
3. First Feeding
Once a portion of the plasmodium has crawled out, place a single flake of oatmeal a few millimeters ahead of its path. When the slime mold senses the food’s scent (compounds from starch and yeast), it accelerates its protoplasmic streaming in that direction, enveloping and feeding on the oatmeal within a few hours.
4. Daily Maintenance and Mold Control
As the slime mold grows, it can crawl several centimeters a day, sometimes climbing up the walls and onto the lid of the petri dish.
- Maintain Moisture: Add 1 to 2 drops of water daily (e.g., using a spray bottle) to keep the paper damp.
- Adding Food: Once the oatmeal is enveloped by the yellow slime mold and becomes mushy, place a new flake of oatmeal in a separate spot. If the old food begins to mold, use tweezers to cut out the surrounding paper and discard it.
- Mold Rescue: If mold starts growing faster than the slime mold, gently pinch a healthy, bright yellow tip of the plasmodium with tweezers and transfer it to a new, damp petri dish to save your culture from crashing.
⚖️ 4. Behavior Patterns: Three Different Life Stages
Depending on environmental conditions, slime mold morphs into three entirely different life stages.
| Stage | Characteristics | Role | Rearing & Observation Tips |
|---|---|---|---|
| Plasmodium | Yellow, pulsating, amoeba-like form. Crawls actively and eats voraciously. | Growth & Feeding Phase | Requires proper humidity and food (in the dark). Sensitive to dryness and light. |
| Sclerotium | Hard, reddish-brown to dark brown mass formed when moisture is lost. | Dryness Resistance / Dormant Phase | Can survive without water for months or years. Revives within hours once water is added. |
| Sporangium (Fruiting Body) | Clusters of tiny mushroom-like spore cases. Produces black/gray dust. | Reproduction / Spore Dispersal Phase | Occurs when food is depleted or triggered by light and temperature changes. Cannot revert back. |
🌟 5. Slime Mold Network Design and Maze-Solving Experiments
Once your slime mold is stable and active, you can perform simple behavioral biology experiments at home.
Figure 2: A comparison of slime mold optimization, narrowing down its veins to the shortest path connecting food sources in a maze constructed with plastic barriers (*Image is for illustrative purposes only)
How to Perform the Maze Experiment
- Create a simple “maze” inside the petri dish using thin plastic sheets or dividers.
- Place oatmeal at both the “start” and the “finish” of the maze.
- Initially, the slime mold will spread thinly across the entire maze. Once it finds the food, it will gradually retract its veins from non-optimal paths, eventually leaving only the thickest vein along the shortest path between the food sources.
- If you record this protoplasmic expansion and vein optimization process via smartphone time-lapse over several hours, you can capture its highly organic and intelligent behavior.
Use your smartphone camera and time-lapse features to hack and witness the “geometric intelligence” spun by a brainless, single-celled organism right before your eyes!
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