What is a Slime Mold? (Hint: It's Not Mold)

Your first blob will look like spilled yellow paint, then slowly crawl across your petri dish. That is normal. Slime mold moves in pulses, feeds on simple food, and changes shape fast as conditions change.

If you came here from Google asking what a slime mold is, here is the short answer. It is a living organism that can move and solve simple problems, but it is not an animal, not a plant, and not a fungus.

What is a slime mold?

A slime mold is a

protist: A eukaryotic organism that is not classified as an animal, plant, or fungus.

. The species most people keep is Physarum polycephalum, often called “the blob.”

The name confuses people because of the word mold. Slime mold was grouped with fungi in older systems, but current biology places it with protists. It still makes spore structures, which is one reason it is often mistaken for a fungus in photos.

The group used in hobby culture is usually called

myxomycetes: Plasmodial slime molds that form a visible, moving feeding stage and later produce spores.

.

What does your blob actually do?

Your blob spends most of its active life in a feeding form called a

plasmodium: A single, giant, multinucleate cell that spreads over surfaces while feeding.

. In plain words, it is one cell with many nuclei that behaves like a moving network.

When food is nearby, the network grows toward it. When part of the network is useful, tubes in that area often become thicker. When food runs out, growth slows and the pattern changes.

When conditions become too dry, your blob can enter

sclerotium: A dry, dormant survival state that can reactivate after moisture returns.

. This is one reason it is practical for home keepers. You can pause a culture and wake it later with moisture.

Is slime mold dangerous?

For home growing, Physarum polycephalum is treated as harmless to people and pets. It does not hunt animals, it does not bite, and it does not behave like an infection.

In a culture setup, your blob mainly feeds on microbes and prepared food like oat flakes. Good hygiene still matters, not because the blob is dangerous, but because food residue can support unwanted contamination.

Why do people say it is “smart”?

Slime mold has no brain and no neurons. Even so, it shows measurable problem-solving behavior in controlled experiments.

In maze tests, it can reduce growth in dead-end areas and maintain efficient connections to food. In repeated-stimulus tests, it can change response timing after repeated exposure. In network experiments, it can build transport patterns that resemble efficient path layouts.

This behavior is one reason slime mold appears in science classes and public exhibits. It is easy to observe and it raises big questions about how simple life organizes information.

What is the “720 sexes” claim?

The short version is that this refers to mating types, not sexes in the everyday human sense.

Different strains can fuse only when their mating-type genetics are compatible. Reports around Physarum polycephalum often summarize this as hundreds of possible mating-type combinations, commonly cited as 720. The main idea for beginners is simple: compatibility is genetically diverse, so pairing options are broad.

What to do next

If this is your first visit, start with setup and feeding so your blob survives the first week.

• Read Getting Started: Your First Blob Setup for container, moisture, and light basics.
• Read The Ultimate Guide to Feeding Your Blob for practical feeding rhythm.
• Read Troubleshooting: When Things Get Sticky if growth stalls or contamination appears.