Toothpaste Slime Mold

   a.k.a.

Wolf’s Milk Slime

   a.k.a.

Lycogala epidendrum

by Holly Schubert

Photo by Lisa K. Suits   from http://mdc.mo.gov/discover-nature/field-guide/wolfs-milk-slime-toothpaste-slime

From time to time we come across these little pink bubbles while walking in the forest with campers or students. They are small, but eye-catching, and people often want to know, “what is that?!” These are commonly known as Toothpaste Slime Mold, sometimes Wolf’s Milk Slime, and their scientific name is Lycogala epidendrum.

Toothpaste slime mold at Lutherlyn, 2014.

They look like funky mushrooms, but slime molds are not really a fungus. In fact, scientists have had a hard time pinning down exactly what they are. The Conservation Commission of Missouri says slime molds “at one time were regarded as animals, then thought to be plants, then fungi. Now, because of DNA studies, slime molds are believed to be closer to the protozoa.”

These organisms are also pretty amazing!

Slime molds like the toothpaste slime mold are known as plasmodial slime molds, and have two main life stages. In the first plasmodium stage, the slime mold is like a huge single-celled amoeba (huge for an amoeba anyhow!), and can creep along on dead plant matter in search of food, consuming bacteria, yeasts, and fungi. (It is this feature of slime molds that was part of the inspiration for the 1950’s horror movie “The Blob”!)

When there is no more food source available, the plasmodium gets ready to reproduce and turns into a fruiting body – essentially a spore sac. This is the second life stage, and this is what we see – in a toothpaste slime mold it appears as little pink bubbles growing on the sides of trees and dead logs. 

toothpaste slime mold at Lutherylyn, 2020.

When immature, its insides are a pink goo that looks a little like toothpaste, hence one of its common names. As the fruiting body matures, the insides dry out and turn brown or gray. The dry spores then disperse on the wind to create more slime molds. The change from pink and spongy with oozy goo inside to dry and gray-brown with a puff of spores inside can take place in a single day. If you see a slime mold and go back to look at it tomorrow, it may be completely gone!

"Pink and brown slime molds" by Benny Mazur from Toledo, OH                Licensed under CC BY 2.0 via Commons -https://commons.wikimedia.org/wiki/File:Pink_and_brown_slime_molds.jpg#/media/File:Pink_and_brown_slime_molds.jpg

So if you see those cute bubble-gum pink bubbles on a dead log, take a close look! And keep in mind that they started out as a “huge” single-celled organism that can move under its own power, consuming food as it oozes along; that its true nature has puzzled scientists for decades; and that it may be gone within a day. Scientists have even seen some slime molds learn from their environment and change their behavior in anticipation of expected conditions! Nature truly is full of weird wonderful beauty!

For further reading:
Wikipedia, Slime Mold
Wikipedia, Lycogala epidendrum
Missouri Department of Conservation, Wolf’s Milk Slime (Toothpaste Slime) 
Discover, Slime Molds Show Surprising Degree of Intelligence