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Scientist's Pick: Smart Slime


Note: This month's "Scientist's Pick" is from Science Buddies' staff scientist, David Whyte. David presented this project to the Science Buddies' team last fall. It's very cool! ~ Science Buddies' Editorial Staff

Project: Smarter Than Your Average Slime: Maze-solving by an Amoeboid Organism
Scientist: David Whyte
Science Buddies' Difficulty Level: 7-9

I was doing some background research on simple organisms that might be used in science projects when I came across an article entitled "Maze-solving by an amoeboid organism." The article contained just what I had been looking for—the basis for a novel project that was both cutting-edge science and also well within the reach of the kitchen scientist.

Materials Tip!

Kits for growing the organism, Physarum polycephalum, can be purchased from several science supply stores online.

The basic finding of the research presented in the article was that Physarum, a common inhabitant of wooded areas around the world, can find the shortest path through a maze set up on an agar plate. Physarum, also called slime mold, typically forms a large amoeba-like mass that moves over dead leaves and rotting logs looking for organic matter to consume.

Announcing their findings in the journal Nature, the researchers said they believe the organism changed its shape to maximize its foraging efficiency and therefore its chances of survival. They went on to claim that "This remarkable process of cellular computation implies that cellular materials can show a primitive intelligence."

In the lab, Physarum can be grown in Petri dishes that have a layer of agar on the bottom, so I decided to put Physarum to the test at home.

Conducting the Experiment

To set up the experiment, I placed pieces of slime mold in a 30-square-centimeter (five-square-inch) maze on an agar plate. On that same plate, I strategically placed a food source at two spots in the maze.

What happened?

The pieces of slime mold coalesced, and the organism condensed its entire body to form a mass that stretched between the two food sources and connected them. In each trial, the slime mold showed its ability to both solve the maze and find the food. Each time, it adopted the shortest possible route, effectively solving the puzzle.

The project idea I created for Science Buddies lets you devise your own maze to see for yourself how the slime mold behaves. You'll have to decide for yourself—is the slime mold "intelligent"? Are there limits to its intelligence?

Other questions you might ask as you work with the Physarum include:

  • What environmental cues is it using and how does it process information in ways that allow it to adapt?
  • What other tests can be devised to further explore how these remarkable creatures respond to the world as their senses experience it?

For me, any project that involves "cellular computation" and "primitive intelligence" in an amoeboid organism has lots of potential. In this project, what I discovered is that Physarum is a simple organism - one that you can experiment with at home—but it is not really so "simple" after all.


If this project sounds like fun, you might want to explore other Project Ideas in our Zoology section.


Our school system participates in the Intel International Science & Engineering Fair (ISEF), so our science fair projects must follow ISEF safety rules. Although slime mold is about as harmless as it gets, it's still classifed as a Biosafety Level 1 (BSL-1) substance. Working with Physarum requires approval from a Scientific Review Committee before data collection -- and a student must culture it in a BSL-1 approved lab. So this experiment may be at a level that a "kitchen scientist" can handle, but not every school science fair program allows live organisms to be handled at home in the kitchen!

Because we're new to the school science fair this year, and because the rules are lengthy and detailed, my son Will found all this out at the eleventh hour -- just as we were about to start culturing and collecting data at home. He & his teacher are very enthusiastic about the project and his variation on it, though; so we're working hard to get the paperwork done and find an approved lab. Hopefully, the worst complication will be that we'll need to order a fresh culture to use in collecting the data for the project.

It's a great idea, though, and the experiment really captured Will's imagination. We hope to get the technicalities worked out in time to allow him to participate in the school science fair.

Thanks for suggesting such a fun project!

Hi Will's Mom:

It sounds like your son is having a good science experience and a real-world run in with red-tape! We agree, slime mold is a perfectly harmless organism that is safe for 'kitchen science.' But your story is a good reminder that different science fairs have different rules. We'll do our best to prevent others from having the same troubles by reminding our users to check with their local chapters before proceeding.

"Bravo" for your son's perseverance though! We hope he manages to complete the repeat in time. If you're still looking for a BSL-1 lab, try contacting the biology departments of local universities or 2- and 4-year colleges. They have the facilities and may be able to accommodate your request.

We'd love to know what your son's variation was. Maybe it is even one we could add to the Variations section of this project! If you are interested in sharing it with us, you can reach us at scibuddy @ sciencebuddies.org.

Best of luck!

~ Science Buddies

Will got permission to work at home, and finished his first trial last week. Only one of six samples reached the oatmeal - but it did so by the shortest path (78mm)! Although he didn't get the data needed to test his hypothesis yet, he was able to measure the speed of growth through the mazes. That data suggests that Physarum goes downhill SLIGHTLY faster than it goes uphill. He's starting another culture, and in a few days will conduct another trial. He hopes to have time for 3 trials before the final project is due.

In a slightly creepy episode, Sample E stretched a pseudopod out across the outer boundary of the maze one night. The next morning, the entire body of the culture had jumped out of the maze and had migrated about a centimeter away from it - presumably having "decided" that there was no food for it in the maze! Now THAT sample was indeed smarter than the average slime.

Hi Will and Will's Mom - Thanks for letting us know how things are going. We're glad to hear the slime revived and that his first trial showed some smart slime! The Sample E slime does sound a bit too clever! We hope the other trials go well and give the data he needs.

Science Buddies

Will's physarum project took 1st place in the microbiology category of the school science fair last night, and he's on to the county competition in February!

Will conducted 3 trials (18 specimens) with his slime mold. Each trial ran 60-80 hours. Only 1 specimen reached the oatmeal via the maze. Another specimen climbed over the maze walls (probably the agar was too warm when he attached the maze, & liquid agar splashed onto it); this specimen went directly to the target oatmeal. The other 16 specimens failed to travel through the entire maze. However, Will was keeping regular measurements of the specimens' progress & was able to observe the effect of gravity on physarum (geotaxis).

We noted the following challenges in the project:
- The mazes were extremely difficult to cut, even with an x-acto knife.
- The oatmeal agar developed fuzzy white or black mold after about 4 days. While it could be scraped off, it returned very quickly. This may have happened because Will had to take the lids off the petri dishes every few hours to make observations.
- The specimens grew and traveled MUCH more slowly (around .15mm/hour) than the literature review led us to expect. This may have been a result of growing conditions or the "health" of the specimens we purchased.

If Will decides to run more trials in preparation for the county science fair, he will probably practice culturing slime mold to determine optimal growing conditions for it before he conducts new trials in mazes.

It was a wonderful experiment! His teacher & class loved hearing about it, and several of the kids wanted to know if they could grow slime mold as a "pet."

Congratulations! We're thrilled to hear about Will's success with the project and at the school fair. We wish him much luck in the county competition, and we'll look forward to hearing how it goes. Thank you for sharing feedback on the experimental procedure.

~Science Buddies

My name is Najah, and i am a freshman, trying to start my Physarum Polycephalum science experiment. It is very challenging for me because i really dont know the best way to test two food sources. Meaning that i dont know what other food source that i need. I already have oatmeal but im not completely sure what other food source is needed. Can you please help?

Hi Najah - This can be a really great project to work on! If you have the oatmeal, then you are all set with food to try the project using the Experimental Procedure in the Project Idea. Are you envisioning changing the project to measure something "else" based on two different food sources? You can get input from our team of Experts in the Ask an Expert forums. To register for a free account, visit: http://www.sciencebuddies.org/science-fair-projects/ask_an_expert_intro.shtml

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