Obscure Oozing Oddities: The Overlooked World Of Slime Molds

Aug 24, 2015

Slime molds are stubbornly mysterious. They are usually lumped in with fungi, but exhibit several traits ordinarily attributed to animals. One of these stands out above the others: slime molds travel.

On a recent walk through dry woods, I glanced down at a fallen ponderosa pine. Stuck to its side was a cluster of small pink balls, the color of bubble gum and half the size of marbles. Looking closer, I saw brown globules there as well. Thinking I’d found some of the round mushrooms known as puffballs, I dug my pocket knife into the moist wood beneath them, looking for the web-like fungal strands that should underlie a puffball. I found…nothing. I dug some more. Still nothing. What was this stuff?

Later I learned that, regardless of its puffball-like appearance, the specimen in question wasn’t a mushroom at all. It was Lycogala epidendrum, a member of a strange group of organisms known, rather unfortunately, as slime molds.

Slime molds are stubbornly mysterious. They are usually lumped in with fungi, but exhibit several traits ordinarily attributed to animals. One of these stands out above the others: slime molds travel. Individuals can be found creeping about like giant amoebas on logs, trees, leaf litter, and just about anywhere their bacterial food is found. A few years ago in Great Smoky Mountains National Park, the park newsletter issued daily bulletins about the progress of a slime mold that was oozing up the trunk of a tree near park headquarters at the rate of several inches a day.

Some slime molds have journeyed around the world, though not by oozing. They spread far and wide by dispersing their microscopic spores on the wind. The Lycogala epidendrum I encountered on an island in Flathead Lake has been found everywhere from Brazil to Barrow, Alaska. It may be one of the most cosmopolitan species on earth. Although slime molds generally live in cool, damp places, nearly fifty species have been reported in the desert Southwest, living wherever they can find a tiny bit of moisture.

A slime mold spends most of its life as a wandering mass called a plasmodium. They are often colorless, but can be bright yellow, orange, or red. Some live inside decaying logs and other plant material, while others crawl about on the surface. When it is time for a plasmodium to reproduce, it relocates to a drier and more exposed location. Gathering itself into a clump, it undergoes a remarkable transformation in which its entire body is changed into spore-producing structures.

Scientists who specialize in slime molds prefer to call them by the more technical name myxomycetes. Individual species are also referred to by their scientific names, and one author of a text on slime molds goes so far as to say that “myxomycetes do not have common names.” Field guides, however, do list common names.

I first knew my mystery mold by its English name: ‘wolf’s milk slime.’ Perhaps scientists suppress the common names because they despair of ever fostering affection among the general public for organisms with monikers like ‘many-headed slime,’ ‘yellow-fuzz cone slime,’ or, worst of all, ‘dog vomit slime.’ As you probably guessed, slime molds get their common names from their appearance. An unsettling number relate to food: you might encounter ‘red raspberry slime,’ ‘carnival candy slime,’ ‘pretzel slime,’ ‘tapioca slime,’ and even ‘scrambled egg slime.’

A spectacular display of this last species caused quite a stir in Texas in 1973, and even made the national news. Suburbanites awoke to find large pulsating yellow masses skulking on their lawns. Rumors flew about alien invaders and mutant bacteria. Fortunately, the yellow goo vanished before the National Guard could be mobilized.

Slime molds are rarely on our minds, much less on the news. When we walk through the woods, we tend to look for the large and spectacular. But I’m glad I looked down that day in September. I was reminded that the strange and obscure can be pretty spectacular as well.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Fieldnotes," 8/9/15. You can hear the program on the radio Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or listen via podcast.)