The Day 'Dog Vomit' Slime Mold Invaded My Front Yard

It looked like something out a a horror film: a vivid, yellow, blob-like substance appeared to be oozing across our garden mulch. Upon further research, I discovered that I had slime mold in my garden, the kind affectionately known as "dog vomit."

This yellow slime mold is preparing to transform into fruiting bodies. Photo by Emily Johnson.

About a week ago, we noticed an intruder in our front yard -- a vivid, yellow, blob-like substance that appeared to be invisibly oozing across our garden mulch like the beginnings of a horror film. My first thought was naturally, will it creep into my house through the windows, consume my family and then feed on our brains?

But upon further research, I discovered the culprit -- slime mold. I had slime mold in my garden. And not just any kind of slime mold. The kind affectionately known as "dog vomit." The nickname took on new meaning when I found that the bright yellow bumps had transformed overnight into a lumpy brown pile that looked precisely like our beagle-boxer mix had gotten sick in the yard.

Slime mold Slime mold is harmless to humans and removing it is as easy as packing it in a plastic bag and tossing it. Be careful not to spread it and don't spray it with water as its spores may spread. Photo by Jenny Marder

Like any homeowner, I was thoroughly grossed out and wanted it gone. But like any decent journalist, I needed some pictures first. Plus, I had no idea what to do with the stuff. Was it dangerous? Was it harmful to touch? To breathe? So I took a trek to my local garden shop for guidance.

Yes, they'd heard of slime mold. In fact, nearly every employee I talked to at the Merrifield Garden Center had encountered slime mold in their own yards at some point. And to my relief, their brains seemed very much intact.

Tim Guy, a manager and horticulturist there, told me he's had it three or four times, and every 200 or so customers come into the store inquiring about it.

"They go, 'it looks like someone threw up in my yard,'" he said. One time, he saw it run over a patch of low azaleas and kill them.

Its origins are in the trees that make up the mulch, he explained. Bacteria gets on the tree bark when they're dragging it through the woods. Though the mulch gets sterilized, some of the spores sometimes survive.

For more basics, I turned to Steven L. Stephenson, a research professor at the University of Arkansas and an expert on slime molds.

View Slide Show Slime mold forms in various shapes and colors. Watch a slide show of some of the more stunning accumulations.

A slime mold, he explained, is a soil-dwelling, single-celled, "fungus-like organism typically associated with decaying plant material, where they feed on bacteria." There are more than 900 species of slime molds, they are found on every continent and they thrive in moist, shady places.

"A compost pile represents one of the best possible places to find them and it is unlikely that one could find a compost pile without slime molds present," he wrote in an email.

When food is scarce, the single-celled organisms combine, grow and spread in a multicellular mass, like an organized dance. Once that mass is formed, the cells reconfigure their function to form stalks, which produce bulbs called fruiting bodies. These fruiting bodies contain millions of spores, and these spores can get picked up and transported by wind, an insect or an animal. There, they start the process all over again as single-celled organisms. (See Rebecca Jacobson's April 2012 story for more on this.)

Most importantly, Stephenson stressed, they are completely harmless.

"People who find a slime mold in their yard shouldn't be concerned at all," he said. "They should realize that slime molds are some of the more interesting and fascinating organisms found in nature. Since slime molds are microorganisms throughout most of their life cycle, and microorganisms are too small to be observed directly in the field, they literally give us a window into the world of microbial ecology."

So there it is. I was not haunted by slime mold. I was one of the lucky ones. The slime mold had chosen me. I had a virtual window into microbial biology dwelling in my very own front yard. And that's where it would remain until I returned home to destroy it, mercilessly.

Back at Merrifield, the advice was simple and strict. Using a pitchfork, they instructed me, gingerly move it to a plastic bag and toss it. Disturb it as little as possible. And do not, they stressed, under any circumstances, spray it with water. That spreads the spores.


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