The slime mold as a pet: everything you need to know before adopting one
Adopting a slime mold means welcoming the strangest organism on the planet: 720 sexes, no brain, and a lineage over a billion years old. A complete guide before you get started.
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The blob is arguably the strangest pet you could ever adopt. Not a dog, not a cat, not a fish — a giant single-celled organism, from a lineage far older than animals. Here is everything you need to know before you get started.
Is a blob a real pet?
Technically, the blob (Physarum polycephalum) is neither an animal, a plant, nor a fungus — it belongs to the supergroup Amoebozoa. But in practice, yes: you adopt it, you feed it, you name it, you observe it. It can be considered a fascinating scientific companion, especially for children aged 7 and up.
Why adopt a blob instead of another pet?
5 reasons that make the difference
- 🧬 720 mating types — not "sexes" in the animal sense, but compatibility types: matA (16 alleles) × matB (15) × matC (3) = 720 combinations
- 🧠 No brain, yet it solves problems — mazes and network optimization (Nakagaki 2000, Tero 2010)
- 📅 A very ancient lineage — Amoebozoa date back over a billion years according to molecular clocks. The age of the species itself is not datable: myxomycetes almost never fossilize
- 🌍 No known health risks — no human infections described in the literature
- 🛌 Pause mode: going on vacation? You sclerotize it and it waits for you, dry, without needing any care
"720 mating types" 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.
The blob is genetically closer to animals than to plants. The amoeboid lineage is very ancient, far predating the Cambrian explosion. Be careful, however, not to confuse the age of the lineage with that of the organism: the blob that arrives at your place is just a few weeks old.
Source: Adl, S.M. et al. (2019). Journal of Eukaryotic Microbiology, 66(1).
What do you have to do day-to-day?
The routine for an active blob (plasmodium)
| Frequency | Action | Duration |
|---|---|---|
| Every 2 days | Add 2-3 oat flakes | 30 seconds |
| Every 2-3 days | Check the state of the agar (signs of mold, dried-out agar) | 1 minute |
| Every 4-5 days | Transfer a piece of blob to fresh agar | 5 minutes |
| Whenever you want | Observe, photograph | Unlimited |
Ideal environmental conditions
- Temperature: 19-25 °C (standard indoor temperature). Below 18 °C it slows down significantly; around 15 °C it may seem completely stopped for several days — it isn't dead, it's just waiting for warmer weather.
- Humidity: the agar in a closed Petri dish maintains humidity on its own
- Lighting: dim (the blob avoids direct light)
- Location: on a desk, a shelf, away from drafts
How long does a blob live?
The blob has no programmed aging like an animal: it can alternate between an active form (plasmodium) and a dormant form (sclerotium) for a very long time, provided it is maintained.
In practice at your home
- Active plasmodium: you can keep it for several months, but only if you transfer it regularly to fresh agar (about every 4-5 days). Without transfers, a single dish lasts a few weeks: the blob depletes the substrate, waste accumulates, and it eventually sclerotizes.
- Sclerotium form (dormant): kept dry and away from light, a sclerotium remains viable for at least a year, often much longer. For this reason, BlobFarm kits include 90 mm Ø filter papers that allow you to properly re-sclerotize your blob whenever you want to put it on pause.
- Complete cycle: you can have it alternate between the two states for years
"A well-maintained blob has no expiration date: it alternates between active phases and dormancy as long as you keep up with the transfers."
Blob vs. classic pets: matchup
| Criteria | Blob | Goldfish | Cat |
|---|---|---|---|
| Purchase price | €18-68 | €3-5 | €0-1500 |
| Maintenance / year | A few euros for agar and oats | Aquarium, filter, food | Several hundred euros |
| Lifespan | Several months to years, with regular transfers | 5-10 years | 12-18 years |
| Vacation | Put on pause | Pet-sitter | Pet-sitter |
| Allergy risk | No known allergens to date | None | High |
| Space | Petri dish (10 cm) | Aquarium (50 L) | House |
| Noise | None | None | Variable |
| Educational value | ⭐⭐⭐⭐⭐ | ⭐⭐ | ⭐⭐⭐ |
Who is it for?
✅ The blob is perfect for
- Families with children aged 7 and up who are curious about science
- Teens/adults passionate about biology, mycology, natural sciences
- Primary school (ages 7-11) and middle school teachers
- People allergic to pet dander
- Tenants with leases forbidding classic pets
- Students in small apartments (one blob = 10 cm × 10 cm)
- Science content creators (Instagram, TikTok, YouTube)
❌ The blob is not for you if
- You are looking for an animal to cuddle (the blob should not be touched)
- You want a companion that recognizes you
- You expect emotional interaction
Is the blob dangerous?
No — but let's be precise, because there is a lot of misinformation on this subject. P. polycephalum is not associated with any human infection in the scientific literature, and does not appear on any European regulatory list of at-risk biological agents.
- No known allergens to date
- No known toxicity — can be handled with bare hands, hand washing is simply for hygiene
- It is not for consumption, obviously: neither the blob nor the agar
- No documented risk for pets
The real points of caution for the kit
Spoiler: it's not the blob.
- No sharp objects — and that is intentional: our kits do not contain them. The tools are tweezers and spatulas — never a blade or scalpel. The blob is sampled and transferred with a spatula, never with a blade.
- Contamination mold — if a dish gets covered in green, black, or white fluffy fuzz, close it and throw it away without opening it near your face, then wash your hands. This has nothing to do with the blob; it is standard culture contamination.
Finally, for pregnant women and immunocompromised individuals: no contraindications are documented, but we are not doctors — if this applies to you, simply ask your own doctor.
More info: Is the blob dangerous? Health risks explained
The blob, a star of French education
In 2021, the CNES launched "Élève ton blob" (Raise your blob) in parallel with Thomas Pesquet's Alpha mission. Around 4,500 institutions applied, and nearly 2,000 were selected to conduct the experiment on the ground. Since then, the blob has become one of the most popular educational organisms in primary and middle schools.
How much does it really cost day-to-day?
With a BlobFarm kit at €23.90 (Classic), a bag of organic oats, and an agar refill, you can go for several months without buying anything else. The maintenance budget for a blob is just a few euros per year — incomparable to an aquarium or a cat.
→ Read our complete budget guide
FAQ — The blob as a pet
Can you take a blob with you on vacation?
Yes, but it is easier to sclerotize it before you leave: kept dry and away from light, it will wait for you without needing any care. You wake it up upon your return by dipping it briefly in a shallow pool of water, shaking it well, and then placing it on agar.
Do you need a permit to adopt a blob?
No, the blob is not regulated. No CITES, no certificate of capacity, no declaration at the town hall. It is a living organism legal everywhere in France and the EU.
Can you adopt several blobs together?
Yes — and it's actually fascinating. Two compatible blobs that meet fuse into one. You can also separate them: a blob cut in two results in two autonomous blobs.
What should I feed my blob?
Oat flakes, and nothing else. Definitely no chocolate or sugar: sugar creates osmotic stress comparable to salt, and it turns your closed dish into a mold factory in two days. Oats are all it needs.
What should I do if my blob dies?
If the plasmodium seems dead (dehydrated, blackened), it may simply be in the process of sclerotizing. Leave the dish closed and wait 24-48 hours. The same applies if it stops moving while the room is cool: below 18 °C it slows down significantly. If it is truly dead, BlobFarm will send you a free sclerotium (waking guarantee).
Can the blob escape?
No. It moves a few millimeters to a few centimeters per hour — faster when it is hungry — and it cannot tolerate dry air outside of its dish. It will never leave its Petri dish on its own.
