Why Slime Mold Records Matter
Physarum polycephalum regularly breaks our expectations of what a single cell can do. It is not just a curiosity for biologists; the extreme capabilities of slime mold challenge fundamental assumptions about the limits of life. Each record documented here reveals something important about biology, physics, or evolution.
The numbers below are drawn from published scientific literature, documented laboratory observations, and verified field reports. Where estimates vary, the most conservative reliable figure is given.
Record: Largest Single Cell
| Metric | Value | Context |
|---|---|---|
| Largest documented Physarum polycephalum | ~5.5 square meters (about 59 square feet) | Laboratory culture, Audrey Dussutour's lab, CNRS Toulouse |
| Largest wild myxomycete | Estimated up to several square meters | Fuligo septica aethalia can exceed 0.5 m across; plasmodia likely extend further |
| Typical laboratory size | 10 to 30 centimeters across | Standard petri dish culture on oat flakes |
To put this in perspective: a 5.5-square-meter Physarum plasmodium is a single cell larger than a king-size bed. It contains no internal cell walls, just one continuous mass of cytoplasm with millions of nuclei. No other known single cell comes close to this size.
Record: Number of Nuclei
| Metric | Value | Details |
|---|---|---|
| Maximum nuclei in a single plasmodium | Estimated hundreds of millions | A large laboratory culture; exact counts are impractical but estimated from nuclear density per unit area |
| Nuclear density | ~50 to 100 nuclei per 100 micrometers of vein | Measured in laboratory cultures using fluorescence microscopy |
| Synchronous division | All nuclei divide simultaneously every 8 to 10 hours | One of the most precisely synchronized biological events known |
The synchronous nuclear division of Physarum is so precise that it has been used as a model system for studying the cell cycle. All nuclei in a plasmodium, whether there are thousands or millions, enter mitosis within minutes of each other. This level of coordination in a single cell with no nervous system is extraordinary.
Record: Movement Speed
| Metric | Value | Conditions |
|---|---|---|
| Maximum recorded speed | Up to 4 centimeters per hour (some reports up to 5 cm/h) | Actively foraging toward food in optimal conditions (25 degrees C, high humidity) |
| Typical cruising speed | 1 to 2 centimeters per hour | Normal exploration without strong attractant |
| Minimum speed | Near zero | In cold conditions or when no stimuli are present |
| Cytoplasmic streaming rate | Up to 1.35 millimeters per second | Internal flow speed, the fastest known cytoplasmic streaming in any organism |
Physarum holds the record for the fastest cytoplasmic streaming of any known cell. The shuttle flow that propels cytoplasm through the vein network reaches speeds of 1.35 mm/s, roughly 100 times faster than streaming in typical plant cells. To learn more about the mechanics, see our page on how slime mold moves.
While 4 centimeters per hour may not seem impressive compared to animal movement, consider that this is a single cell flowing across a surface without any muscles, bones, or legs. Scaled to human body length, the equivalent speed would be competitive with a casual walking pace.
Record: Survival in Dormancy
| Metric | Value | Details |
|---|---|---|
| Maximum verified revival from sclerotium | Over 2 years in controlled storage | Dried sclerotia stored at room temperature; revived with water and food |
| Anecdotal maximum | Possibly decades | Herbarium specimens reportedly revived after very long storage, though verification is limited |
| Spore viability | Estimated 50 to 75 years or more | Myxomycete spores from old herbarium collections have germinated successfully |
| Conditions survived in dormancy | -20 degrees C to +40 degrees C; near-complete desiccation | Sclerotia are among the most resilient biological structures known |
The ability of Physarum to enter sclerotium and survive for years without food, water, or any metabolic activity is one of its most remarkable traits. This is the same property that allowed dried slime mold to travel to the International Space Station and revive successfully in orbit.
Record: Maze-Solving Speed
| Metric | Value | Source |
|---|---|---|
| Time to solve a simple maze | Approximately 4 to 8 hours | Nakagaki et al. (2000), using a 30 x 30 cm maze |
| Method | Fills maze, then prunes to shortest path | Confirmed by multiple labs |
| Accuracy | Consistently finds shortest or near-shortest path | When multiple paths exist, selects optimal in most trials |
The maze experiment remains one of the most iconic demonstrations of slime mold intelligence. The organism does not try paths one at a time like a computer algorithm. Instead, it fills the entire maze simultaneously, then withdraws from dead ends, leaving only the optimal path. This parallel exploration strategy is what makes Physarum so valuable as a model for bio-inspired computing.
Record: Network Optimization
| Metric | Value | Context |
|---|---|---|
| Number of food sources connected optimally | Up to 36 in published experiments | Tero et al. (2010), Tokyo rail map experiment |
| Network efficiency vs engineered systems | Comparable to Tokyo rail network | Matched on cost, efficiency, and fault tolerance |
| Time to form optimized network | 24 to 48 hours (depending on scale) | Laboratory conditions |
The fact that a single cell can produce a transport network rivaling one designed by teams of engineers over decades remains one of the most striking findings in slime mold research. Read more about this on our Tokyo experiment page.
Record: Reproduction Numbers
| Metric | Value | Details |
|---|---|---|
| Spores per fruiting body | Tens of thousands to hundreds of thousands | Varies by species; Fuligo septica aethalia produce millions |
| Fruiting bodies per plasmodium | Hundreds to thousands (from a large plasmodium) | Each sporangium produces its own spore batch |
| Total spore output from large specimen | Potentially billions | A large Fuligo septica aethalium can produce an astronomical number |
For a full discussion of the reproductive cycle, including sporulation, mating types, and the conditions that trigger fruiting, see our dedicated page.
Record: Sensory Capabilities
Despite having no sensory organs, Physarum polycephalum can detect and respond to an impressive range of stimuli:
- Light: avoids blue and UV light; may be attracted to red light in some conditions
- Chemicals: detects food molecules, repellents (salt, quinine), and chemical gradients at very low concentrations
- Temperature: responds to temperature gradients; prefers 22 to 25 degrees C
- Humidity: grows toward moisture and away from dry conditions
- Vibration: responds to mechanical stimulation
- Gravity: uses gravitational cues for orientation (as demonstrated by altered behavior in microgravity)
No other single-celled organism is known to detect and respond appropriately to as many different environmental variables simultaneously.
Record: Memory Without a Brain
| Memory Type | Duration | Mechanism | Source |
|---|---|---|---|
| Anticipatory behavior | At least 3 cycles of periodic stimulus | Unknown; possibly biochemical oscillators | Saigusa et al. (2008) |
| Habituation memory | Transferred to naive organism via cell fusion | Chemical signals in cytoplasm | Vogel and Dussutour (2016) |
| Spatial memory (slime trail) | Indefinite (as long as trail persists) | Extracellular mucus marking | Reid et al. (2012) |
The discovery that slime mold can form and transfer memories without any neural tissue was a landmark finding. The 2016 habituation study by Vogel and Dussutour showed that a slime mold trained to ignore a repellent (salt or quinine) could transfer that "knowledge" to an untrained blob simply by fusing with it. This demonstrated that memory in Physarum is stored as a chemical substance in the cytoplasm.
Other Remarkable Numbers
- Genome size: approximately 210 million base pairs, distributed across an estimated 40+ chromosomes
- Mating types: Physarum polycephalum has at least 29 different mating types (compared to 2 sexes in most animals)
- Known species: roughly 1,000 described myxomycete species, with potentially hundreds more undiscovered (see our species guide)
- Age of the lineage: myxomycetes are estimated to have existed for at least 500 million to 1 billion years, making them far older than most animal groups
- Temperature range: active growth occurs between roughly 10 and 30 degrees C; survives far wider extremes in dormancy
Putting the Records in Perspective
What makes these records truly remarkable is the context. Physarum polycephalum achieves all of this as a single cell with no brain, no nervous system, no muscles, and no specialized organs of any kind. Every record listed here, from the largest single cell to the fastest cytoplasmic streaming to transferable memory, emerges from the physical and chemical properties of one continuous bag of cytoplasm.
This is what continues to draw scientists from fields as diverse as computer science, physics, and philosophy to study slime mold. It forces us to reconsider what complexity, intelligence, and even individuality really mean in biology.
For more astonishing facts, visit our slime mold fact sheet, or explore the full scope of slime mold intelligence.
Records Still Being Investigated
Several potential records remain under active investigation by researchers around the world:
- Maximum growth rate: under ideal conditions (abundant food, optimal temperature and humidity), how fast can a plasmodium double its biomass? Current estimates suggest doubling times as short as 24 hours, but rigorous measurements across standardized conditions are still being compiled.
- Maximum altitude: myxomycetes have been found at elevations exceeding 4,000 meters in alpine environments. Surveys in the Himalayas and Andes may push this record higher.
- Deepest habitat: slime molds are primarily surface organisms, but amoebae (the feeding stage between spore germination and plasmodium formation) have been found in soil samples from surprising depths.
- Oldest viable culture: some laboratory strains of Physarum polycephalum have been maintained through continuous subculture since the 1960s. Whether genetic drift has altered these strains significantly compared to wild populations is an open question.
- Fastest problem-solving: as researchers design increasingly complex experimental setups (larger mazes, more food sources, dynamic environments), the speed and accuracy limits of slime mold computation continue to be tested.
Each new record reveals another facet of what makes this organism so extraordinary. Whether measured in square meters, hours, nuclei, or mating types, Physarum polycephalum consistently pushes the boundaries of what we thought a single cell could achieve.