Explore the enigmatic world of slime molds

_{|  Story by Meghan McMahon |}

_10/18/2024

Have you ever come across dog vomit in nature? How about scrambled eggs or tapioca slime? You may have without even realizing it because these are all examples of slime molds.

Slime molds are one of those things in nature that are just fascinating, and the more you know about them the more you want to know. The intrigue with slime molds starts with what they are — and aren’t. They aren’t a slime, and they aren’t a mold. They look like a fungus or maybe sometimes a lichen, but they aren’t either of those things either.

What they are was so confounding to taxonomists, the scientists that classify organisms, that they didn’t quite know where to put them within the taxonomic structure. In the end, they were placed in the kingdom Protista, one of five kingdoms in the taxonomic structure, along with Animalia (animals), Plantae (plants), Fungi (mushrooms and fungi) and Monera (bacteria). The Protista kingdom is a bit of a catch-all for unrelated organisms that are eukaryotic (meaning they have an enclosed nucleus) and don’t belong in any of the other kingdoms, according to the National Park Service.

Their classification is also unusual in that some slime molds are closely related while others are only distantly related to the hundreds of other slime molds that exist. Even their behavior can be confounding to scientists because while some slime molds live solitary lives as individual cells, others will sometimes join together to work as one when certain chemical signals are received or conditions are suitable, PBS reports.

There are three types of slime molds: cellular slime molds, plasmodial slime molds and slime nets, also called Labyrinthulomycota. Cellular slime molds start as single-celled protists that then come together to form a swarm of cells once a chemical signal is released, according to the University of California-Berkeley.

Both cellular and plasmodial slime molds are of great interest to scientists, but for different reasons. Plasmodial slime molds help researchers see and understand the movement of the contents of cells because it can be seen even with low magnification. Cellular slime molds help cellular and developmental biologists understand how cells interact to create multicellular organisms.

It's easier to define slime molds by what they aren’t than what they are, but slime molds are single-celled organisms that live in the soil, according to PBS. More than 900 species of slime molds exist, and they can be found in just about every color except — interestingly enough — true green. Slime molds can’t be green because the don’t have chlorophyll, the pigment that makes leaves and other living organisms green.

Color isn’t the only thing that is varied among slime molds. They take on many different shapes too. Some are plump and rounded like berries are, while others look like blobs without definitive shapes. Still others look like honeycomb or have a lattice pattern, PBS reports. Some are so small they are microscopic; others grow to be huge, measured in feet not inches or millimeters.

Their common names are often a clue as to what they look like. Scrambled egg slime mold looks a lot like scrambled eggs, and dog vomit slime mold is reminiscent of what you might find when your dog vomits with an empty stomach. Chocolate tube slime mold looks like a collection of tiny cocoa-covered tubes, while coral slime looks like bleached coral. What would you guess red raspberry slime mold looks like? How about pretzel slime mold?

Slime molds are most often seen in moist environments, National Geographic reports. Look for them among fallen logs and damp, rotting wood. At home, you may get lucky enough to see them in spots where you have spread wood chips. In these damp, woody environments they feed on bacteria, fungus and yeast.

Although they are relatively simple structures — they are only a single cell, and they don’t have brains — they are capable of some incredible things, even some things associated with highly intelligent creatures. One such example: They can solve mazes.

According to a 2016 study published in the Journal of the Royal Society, slime molds were not only able to complete mazes but also learn the most efficient way to complete a maze.

This may seem like a useless skill, but it does have some practical applications. One such use is using slime molds to ensure transit systems are optimized for efficiency. Researchers discovered this ability by creating a model of the Tokyo railway system in a Petri dish, using oatmeal to represent all the individual railway stations, The Guardian reports. The slime mold in the Petri dish traveled the shortest, most efficient route to get to the oatmeal — a food source for the slime mold.

Since this discovery, slime molds have been used to test the efficiency of other transportation networks. They’ve also been used to study how to build or rebuild transit networks.

And finding the quickest way to food isn’t the only way slime molds demonstrate intelligence. They also track where they have been while searching for food so they don’t have to retrace their steps, PBS reports. To do this, they leave a slime behind to show themselves where they have been. This slime is similar to what slugs leave behind as they move through their environment.

Slime molds can also learn to endure difficult circumstances in their environment — and teach other slime molds to endure these conditions. This was tested using salt, a substance slime molds will typically avoid, PBS reports. In an experiment, researchers put a slime mold on one side of a small bridge, with food on the other. The surface of the bridge was covered in salt. On the first day of the experiment, it took 10 hours for the slime mold to reach the food, but the time it took to travel to the food grew less with each passing attempt until it took only as long as it took the slime mold in the control test, where no salt was used.

While this demonstrated intelligence does have useful applications to humans, slime molds’ ecosystem role benefits us too. Slime molds are decomposers and help break down and recycle nutrients in the soil that are important to the food web, according to the National Park Service. They are part of the food web as prey too. Soil-dwelling creatures like beetles and nematodes and even some larger animals will eat slime molds.

(Photos via Adobe Stock)