Life cycle of Physarum polycephalum: from sclerotium to plasmodium

Over its lifetime, Physarum polycephalum goes through several radically different forms—to the point where one might think they are distinct species. Here is its complete cycle, step by step, with what you can actually observe at home.

Step 1 — The sclerotium (dormant form)

The sclerotium is the blob's survival form. When conditions deteriorate—drought, hunger, cold—the plasmodium contracts, expels its water, and hardens into a brittle yellow crust. Its metabolism slows to a crawl.

This is the form in which we ship blobs at BlobFarm—each sclerotium arrives placed on a 90 mm Ø filter paper, its dormancy support. Our kits contain several spares: when you want to put your blob on pause, you place it on a new filter paper, and it can sleep for over a year before you wake it up again.

Step 2 — Waking up (24 to 48 hours)

To restart, the sclerotium needs three things: humidity (from the agar), heat (20-25 °C), and darkness. Using tweezers, you dip the sclerotium in a little water, take it out, and shake it well—it should be rehydrated, not soaking wet—then place it on the agar. This is the only time water is involved: afterwards, you never add any more.

Visible timeline

• 0-12 h: nothing visible, rehydration is taking place internally
• ~24 h: first signs on average — a translucent yellow border spills out from the sclerotium
• 24-48 h: clear awakening, the plasmodium fans out
• 48-72 h: it reaches the oat flakes and begins to eat

Step 3 — The active plasmodium

This is the spectacular phase, and it can last for months as long as you feed it and transplant it onto fresh agar.

Plasmodium anatomy

The plasmodium is a single giant cell containing millions of nuclei—no partitions between them. No brain, but a network of pulsing veins where cytoplasm circulates back and forth every 1 to 2 minutes.

"The cytoplasm circulates back and forth every 1 to 2 minutes. It's its version of a heartbeat."

What the plasmodium does

• Moves at a rate of a few millimeters to a few centimeters per hour, faster when it is hungry
• Detects food from a distance (chemotaxis)
• Deploys a vein network that optimizes over time
• Flees from bright light and salt
• Avoids areas it has already explored, thanks to the mucus trails it leaves behind—a form of externalized spatial memory (Smith-Ferguson et al., Journal of Physics D, 2017)

Step 4 — Sporulation

When conditions deteriorate, the blob has two options: sclerotize (survive while waiting for better times) or sporulate (reproduce). Sporulation requires light and hunger: the plasmodium erects mineralized sporangia that release spores. Each spore then germinates into a haploid amoeba—microscopic, mobile, and having nothing in common with the large yellow mass.

Step 5 — Fusion (return to plasmodium)

Two compatible haploid amoebae of different mating types fuse to create a diploid cell, which grows and multiplies its nuclei without dividing: a new plasmodium. The loop is closed.

Observe every step at home

Sclerotium, awakening, and plasmodium can be easily observed at home or in the classroom. Sporulation, however, must be induced—light + fasting—and it is the most difficult experiment of the lot.

Want to follow the cycle over several weeks, with the necessary equipment? The Blob Discovery Kit covers waking up, the active plasmodium, and transplanting across 9 Petri dishes—enough to observe each step in real-time.