Before you begin
All of these experiments use Physarum polycephalum, the most commonly cultured species of slime mold. You will need an active, healthy culture before starting. If you do not have one yet, see our guide to growing slime mold or revive a sclerotium.
For all experiments, work in a clean space, use non-chlorinated water, and keep your setups in the dark unless the experiment specifically involves light. Slime mold grows best at 20-25 °C.
| Experiment | Difficulty | Duration | Key concept |
|---|---|---|---|
| 1. Maze solving | Beginner | 12-24 hours | Problem solving, optimization |
| 2. Food preference test | Beginner | 12-24 hours | Decision making, nutrition |
| 3. Light avoidance | Beginner | 6-12 hours | Phototaxis, stimulus response |
| 4. Memory test | Intermediate | 3-5 days | Habituation, learning without a brain |
| 5. Network building | Intermediate | 24-48 hours | Optimization, graph theory |
| 6. Speed measurement | Beginner | 4-8 hours | Growth rate, measurement skills |
| 7. Fusion experiment | Intermediate | 12-48 hours | Self/non-self recognition |
| 8. Temperature response | Intermediate | 24-48 hours | Thermotaxis, optimal conditions |
| 9. Substrate preference | Beginner | 12-24 hours | Surface interaction, exploration |
| 10. Time-lapse documentation | Advanced | 12-72 hours | Photography, documentation |
Experiment 1: Maze solving
This is the classic slime mold experiment, inspired by Toshiyuki Nakagaki's famous 2000 study. Slime mold can find the shortest path through a maze, a task that would require significant computational power for a computer.
Setup
- Build or cut a simple maze from plastic, cardboard, or agar (see our detailed maze-building guide)
- Place the slime mold at the entrance
- Place an oat flake at the exit
- Cover and keep in darkness
What to observe
The slime mold will initially explore all available paths. Over 12-24 hours, it will retract from dead ends and reinforce the shortest path between itself and the food. The final network connecting entrance to food source closely matches the mathematically optimal shortest path.
Why it works
Physarum uses a decentralized algorithm based on cytoplasmic flow. Tubes that carry more flow (because they are on efficient routes) grow thicker, while underused tubes shrink and disappear. This positive feedback loop naturally selects for the shortest, most efficient connections.
Experiment 2: Food preference test
Does slime mold prefer certain foods over others? This experiment tests whether Physarum can evaluate and choose between different nutrient sources.
Setup
- Place the slime mold in the center of a large Petri dish or container
- Arrange small, equal-sized pieces of different foods at equal distances around it: rolled oats, rice, mushroom, apple, carrot, egg yolk, cheese
- Cover and observe every 6 hours
What to observe
Note which food the slime mold reaches first, which it consumes most, and which it ignores. Physarum generally prefers oats and other carbohydrate-rich foods but also shows interest in protein sources. You can rank the foods by preference and repeat the experiment to see if results are consistent.
Make it scientific
For reliable results, run this experiment at least 3 times with fresh cultures. Record quantities consumed, not just which food was reached first. A food reached first might be closer to a random growth direction, not necessarily preferred.
Experiment 3: Light avoidance
Slime mold avoids light, especially UV and blue light. This experiment demonstrates negative phototaxis in a simple, visual way.
Setup
- Place the slime mold on one side of a Petri dish with oat flakes on the opposite side
- Cover half the dish with aluminum foil, leaving the food side exposed to room light
- Observe every few hours
What to observe
The slime mold must choose between reaching the food (in the light) and staying in darkness. It will typically grow along the darkest available path, hugging the edges and shaded areas. Compare this to a control dish kept entirely in darkness, where the slime mold takes a direct route to the food.
Experiment 4: Memory test
In 2016, Audrey Dussutour and colleagues demonstrated that Physarum can learn through habituation. This experiment recreates a simplified version of their landmark study.
Setup
- Create a bridge between the slime mold and its food using a strip of agar
- Coat the bridge with a bitter but harmless substance: caffeine (from instant coffee powder) or quinine (from tonic water)
- Measure how long it takes the slime mold to cross the bridge each day for 5 consecutive days
What to observe
On day 1, the slime mold hesitates and takes a long time to cross (or avoids the bridge entirely). By day 3-5, it crosses much faster, having "learned" that the substance is unpleasant but not dangerous. This behavioral change, habituation, is a basic form of learning that does not require a nervous system.
Advanced variation
After the slime mold has habituated to caffeine, switch to quinine. Does it cross immediately (suggesting general habituation) or hesitate again (suggesting substance-specific learning)? Research shows the learning is specific to the substance encountered.
Experiment 5: Network building
This experiment recreates the famous Tokyo rail network study, where slime mold built a network connecting food sources that closely resembled the actual Tokyo rail system.
Setup
- Choose a real-world map (your city, a country, a continent)
- Place oat flakes at locations corresponding to major cities or landmarks
- Place the slime mold at the largest city location
- Let it grow for 24-48 hours
What to observe
The slime mold will build a transport network connecting all food sources. Compare the resulting network to actual road, rail, or highway maps. You will often find striking similarities, because both the slime mold and human engineers are solving the same optimization problem: connecting points efficiently while maintaining redundancy. See our detailed article on the Tokyo rail experiment.
Experiment 6: Speed measurement
How fast does slime mold actually grow? This simple measurement experiment builds observation and data recording skills.
Setup
- Place the slime mold at one end of a long container (a rectangular food container works well)
- Place food at the other end
- Mark the leading edge of growth every hour using a marker on the outside of the container
- Measure the distances after the experiment
What to observe
Typical Physarum growth rates are 1-4 cm per hour under favorable conditions, though this varies with temperature, humidity, and food availability. Create a graph of distance over time. Is the growth rate constant, or does it speed up as the slime mold gets closer to the food? Most observers find that growth accelerates as the organism detects the chemical signals from nearby food.
Experiment 7: Fusion experiment
When two Physarum plasmodia meet, they either fuse into a single organism or reject each other. This depends on genetic compatibility.
Setup
- Place two pieces of the same culture about 3-5 cm apart on the same agar plate
- Also set up a second plate with pieces from two different strains (if available)
- Observe the contact zone when the two plasmodia meet
What to observe
Genetically identical (or compatible) plasmodia will fuse seamlessly, merging their vein networks into a single organism. Incompatible plasmodia will meet, form a visible boundary line, and refuse to merge. In some cases, one may even retract from the other. This self/non-self recognition happens without any immune system or nervous system.
Experiment 8: Temperature response
Slime mold grows best within a specific temperature range. This experiment maps that range and observes behavioral changes at different temperatures.
Setup
- Prepare 4 identical plates with slime mold and oat flakes
- Place them at different temperatures: refrigerator (4 °C), cool room (15 °C), room temperature (22 °C), and warm spot (30 °C)
- Photograph each plate every 6 hours for 48 hours
What to observe
Growth is minimal or absent at 4 °C. At 15 °C, growth is slow but steady. Peak growth occurs around 22-25 °C. At 30 °C, the slime mold may grow initially but will likely slow down or start forming sclerotium as a stress response. Temperatures above 35 °C are usually lethal.
Experiment 9: Substrate preference
Does slime mold prefer certain surfaces? This experiment tests how substrate type affects exploration behavior.
Setup
- Divide a large container into sections with different substrates: plain agar, damp paper towel, damp wood, damp plastic, damp cotton
- Place the slime mold at the junction of all substrates
- Place identical food on each substrate at equal distances
What to observe
Note which surfaces the slime mold explores most readily and which it avoids. Agar is typically the preferred substrate because it provides consistent moisture and a smooth surface for vein formation. Rough or very absorbent surfaces may slow growth.
Experiment 10: Time-lapse documentation
Time-lapse photography reveals the dynamic, flowing nature of slime mold growth that is invisible in real time. This is both a science and art project.
Setup
- Set up any of the above experiments in a stable, vibration-free location
- Position a camera (phone or dedicated camera) on a tripod directly above the dish
- Use an intervalometer app to take a photo every 1-5 minutes
- Maintain consistent, indirect lighting throughout
What to observe
When assembled into a video, the time-lapse reveals the pulsing flow of cytoplasm, the exploration and retraction of veins, the optimization of networks, and the overall growth patterns. For detailed photography tips, see our slime mold photography guide.
Recording your results
For any experiment, keep a simple log: date, time, temperature, humidity (if possible), and your observations. Photographs at regular intervals are extremely valuable. This documentation turns a casual observation into real science, and it makes it much easier to repeat and refine your experiments.
Safety and ethics
Physarum polycephalum is not dangerous to humans, animals, or plants. It is not toxic, not parasitic, and not allergenic for most people. However, follow these basic precautions:
- Wash your hands after handling slime mold cultures
- Do not eat the slime mold or the food used in experiments
- Dispose of used cultures by sealing them in a bag and placing in household waste
- If you are using the slime mold for classroom activities, ensure that students with mold allergies are aware of the organism
These experiments represent just the beginning. Physarum polycephalum has been the subject of thousands of published research papers, and new discoveries are still being made. For more about what makes this organism so remarkable, explore our articles on slime mold intelligence and memory without a brain.