Sharing the love of slime molds

Several weeks ago, I was out walking in the yard wondering where the spiders were, when I spotted a bright yellow blob on a large, flat tree trunk. My heart skipped a beat and I rushed to inspect it. Sure enough, it was a resplendent specimen of a healthy dog-vomit slime mold, with nice clumps of protoplasm giving way to fan-like tendrils on one side.

“Hello you gorgeous thing!” I said out loud, wishing my loved ones were with me to share my excitement. They’d understand. When I first learned about slime molds I forced my family to watch YouTube videos and celebrate the wonders of this very strange organism with me. My online students in my “Keeping Up with the Kingdoms” class were appropriately awed as well.

You, fellow readers, have somehow been spared my slime mold fancy up to now. However, the time has come.

Let’s begin.

If you’ve spent any time in the woods, wandering among damp and decomposing logs, you’ve likely encountered a few of the over 900 species of slime molds. Some appear as bright red BB-sized spheres clustering on tree stumps. Some are orange and stringy, like a popped bubble-gum bubble, and some look like bright yellow clumps of scrambled eggs or dog vomit. Likely, you mistook these amorphous blobs as alien fungi from another planet.

If you slowed down to study them, maybe even taking out your phone and pulling up your iNaturalist app to identify them, then followed up with a quick Google search about slime molds, you might have dug deeper into your belief that they are aliens.

So, what are they? Despite the misleading name, slime molds are not molds at all. They are not even in the fungus kingdom. Slime molds are protists, the lovable oddballs of the living world which include algae, amoebas, diatoms, and other organisms that find no home in any other kingdom.

Slime molds spend much of their lives as single-celled organisms, just hanging out living life. But when they find a good source of food, things get freakier than a Cici’s Pizza buffet with chocolate pizza. Some slime molds will begin to grow and divide through a process of cell division called mitosis, which you learned about in middle school. However, they don’t undergo cytokinesis, that final step of splitting into two cells. Instead, they end up fusing into a macroscopic, oozing, giant of a cell with hundreds of nuclei.

Well knock me over with a Biology 101 syllabus. I had no idea that one cell could have hundreds of nuclei.

Now this oozing slime mold will grow and stretch and pulse as it slimes its way around a fallen log, or other host of food. If you are lucky enough to find one in your yard or woods, you might want to check on it daily, watching it shift its shape and position, grow and shrink.

And then one day it will be dried up, with little dots left behind. Those are the new slime molds, all reproduced and ready to begin again.

It’s impressive enough, this oozing, multinucleate mass, but we’ve only just begun.

These brainless blobs exhibit behavior suggesting the complex processes of planning and learning. In labs, researchers situated large petri dishes over maps of cities like Tokyo, and placed bits of oats on the points of interest. Slime molds, set loose in the dishes, detected the food and sent out tendrils to scout the most efficient pathways from one bit of oats to the next, rearranging, extending, withdrawing cytoplasm until the slime mold resembled a map at least as efficient than the public transportation systems laid out by civil engineers, and in some cases, superior.

But wait, there’s more.

Slime molds are repelled by salt, though it’s harmless to them. To test their perseverance, researchers placed salt barriers between slime molds and oats. Eventually, the slime molds couldn’t resist the oats and they crossed the salt bridge. Realizing no harm was done, they boldly oozed through the salt in subsequent trials. Did they learn?

Learning would be a feat for a brainless plasmodium. Passing down learned behavior would also be incredible. And yet, successive generations of these intrepid traveling slime molds also crossed the salt barriers without hesitation.

I am not alone in my appreciation for slime molds. A paper published in The Astrophysical Journal Letters (March 2020) described the work of a team of scientists who are using the growth patterns of slime molds to model the “cosmic web,” which makes up our entire cosmos with interconnected filaments of dark matter.

As for the fabulous specimen in our yard, it began to dry out quickly. After two days, I found a tiny snail munching away on its remains, which pleased me so much that I made a video of it and put it on Tik Tok.

As for the missing spiders, I’m perplexed, and wondering if my orb weavers of last year were just early.

Mary Dansak is a writer and a retired science education specialist living in Auburn, AL. She can be reached at [email protected].

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