What is the blob? Neither animal, nor plant, nor fungus
The blob (Physarum polycephalum) is neither an animal, a plant, nor a fungus. It is a slime mold: a giant cell containing millions of nuclei, originating from a lineage over a billion years old. A closer look.
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When you ask people, "What is the blob?", you hear all sorts of things: a fungus, a mold, a microscopic animal, a carnivorous plant. The truth is more fascinating: none of these terms apply.
The blob, whose real name is Physarum polycephalum, is a myxomycete. Neither animal, nor plant, nor fungus: it is a branch of life that diverged from ours a very, very long time ago—and it has never needed a brain to fend for itself.
A living being that defies categories
Why it's not an animal
An animal is multicellular, with tissues and (almost always) a nervous system. The blob is unicellular: a single giant cell, packed with millions of nuclei. No nervous system. No brain. No organs.
Under exceptional conditions, a plasmodium can cover surfaces on the order of a square meter, in laboratory conditions. In your Petri dish, count on a few centimeters instead—and that is already very good.
Why it's not a plant
Plants perform photosynthesis. The blob, however, is heterotrophic: it feeds on organic matter (bacteria, fungal spores, oatmeal). It does not capture light to produce energy. It actually flees from it when it is bright.
Why it's not a fungus
This is the most common error—and it goes back a long way: for a long time, myxomycetes were classified as fungi because of their sporangia.
The fundamental difference comes down to one word: where digestion occurs. A fungus releases its enzymes into the environment and absorbs the dissolved nutrients: it digests outside. The blob, for its part, engulfs its prey (bacteria, yeasts) and digests them inside its own cell, like a giant amoeba. It can also absorb dissolved nutrients, so it is not a "strict predator"—but no fungus performs phagocytosis.
Add to that the wall: rigid chitin in fungi, a simple flexible plasma membrane in the blob.
So, what is it exactly?
Its place in the tree of life, as described by current classification (Adl et al., 2019):
Eukaryota › Amoebozoa › Evosea › Eumycetozoa › Myxogastria › Physarales › Physaraceae › Physarum polycephalum
Closer to you than to an oak tree
The blob, animals, and fungi share the same broad set: Amorphea. In other words, you are genealogically closer to a blob than to a plant. However, be wary of the phrase floating around everywhere: the blob is not "closer to animals than to fungi." Animals and fungi are closer to each other than either is to the blob.
"The blob is 500 million years old"? No.
You will read everywhere that the blob "existed before the dinosaurs" and "survived five mass extinctions." That's nice, but unverifiable, and we prefer to tell you what we actually know:
- The Amoebozoa lineage dates back, according to molecular clocks, more than a billion years.
- The species Physarum polycephalum, however, cannot be dated: myxomycetes, being soft, almost never fossilize. The oldest confirmed fossil of the group (in amber) is around 100 million years old.
So: a very ancient lineage, yes. A precise figure for the species, no.
The 3 forms of the blob
- Sclerotium (dormant) — a small, dry crust. Stored in a dry place away from light, it remains viable for at least a year, often much longer. This is the form in which we ship it at BlobFarm.
- Plasmodium (active) — the bright yellow form that crawls, spreads its venous network, and eats. Its speed ranges from a few millimeters to a few centimeters per hour, the faster the hungrier it is.
- Sporulation (reproduction) — when conditions deteriorate, it produces fruiting bodies that release spores.
"A giant cell. No brain. And yet it solves mazes."
720 mating types: where does this number come from?
This is the most repeated fact about the blob, and for once, it is solid—provided you know where it comes from. The mating of Physarum is controlled by three independent, multiallelic loci:
matA (16 alleles) × matB (15) × matC (3) = 720 combinations
Source: Kawano, S., Kuroiwa, T. & Anderson, R.W. (1987), "A third multiallelic mating-type locus in Physarum polycephalum", Journal of General Microbiology, 133(9), 2539-2546.
You will sometimes see "8 × 9 × 10": that is incorrect, that doesn't even make 720. And no, the blob does not have "720 sexes" in the sense understood in animals—it has 720 compatibility types, which is not quite the same thing. It remains mind-boggling.
Why it fascinates scientists
The blob has become a laboratory star for a simple reason: it does things that biology told us were impossible without a nervous system.
1859: Anton de Bary describes myxomycetes and links them to animals, under the name Mycetozoa ("animal-fungi") — Zeitschrift für wissenschaftliche Zoologie, 10, 88-175
1987: Kawano et al. establish the third mating-type locus → 720 combinations
2000: Nakagaki shows that the blob solves a maze (Nature)
2010: Tero et al. make it replicate the Tokyo rail network (Science)
2017: Smith-Ferguson et al. describe how its externalized spatial memory, inscribed in its mucus trails, helps it navigate (Journal of Physics D)
2021: the "Raise your blob" experiment from CNES arrives aboard the ISS
And where does the word "blob" come from?
From the cinema. The Blob, an American film from 1958, where a slimy mass from space devours a small town. The nickname was already circulating in the French press in the 2010s; the Paris Zoological Park made it explode among the general public by exhibiting the organism in October 2019.
How to observe it at home
The blob is not reserved for labs. BlobFarm cultivates and ships sclerotia ready to be awakened, along with the agar, oats, tools, and protocol sheet. You briefly dip the sclerotium in a little water, shake it well—rehydrated, not soaked—place it on the agar, put the dish in the dark—and 24 to 48 hours later, you watch a single cell crawl toward its meal.
Two strains to choose from, at the same price: Major Tom (LU352, the strain that went to the ISS) and an Australian isolate of Physarum polycephalum.
