Rains bring out an ancient lifeform

I was on my regular Duluth dog walk last week when I spotted this in a neighbor’s mulch. I’m no expert, but I’m pretty sure this is a slime mold – specifically, “dog vomit” slime mold: Fuligo septica.

This type of slime mold is relatively common on mulch, and sometimes Extension gets questions about it from alarmed homeowners who wonder if it’s toxic or will spread in a hideous mat that takes over the yard and kills plants. It isn’t, and it won’t.

I was delighted to get a chance to see this. Slime molds are fascinating. They look like a fungus or a lichen, but they are not fungi, they are not plants and they are not animals. In fact, they have been around since before plants or animals existed. They’re one-celled creatures that can come together and form a mass which then can make bizarre shapes to get at food and to make spores to reproduce.

Unlike fungi, which stay fixed in one place, slime molds can move around. There’s a fun movie about them, The Creeping Garden, that shows slime molds seeming to behave intelligently, working their way through mazes to reach a food source.

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The aptly named "dog vomit" slime mold often appears on mulch.
Contributed / Catherine Winter
The aptly named "dog vomit" slime mold often appears on mulch. Contributed / Catherine Winter

Slime molds feed on decaying matter, so they commonly appear on mulch, but they can pop up in lawns or on the leaves of plants, too. They can be unsightly, like this one, but they’re not hurting anything, except that on grass or other plants they may block the sunlight the plant needs. Slime molds appear when the weather conditions are right, so the recent rain we’ve had probably drove this one to do its thing. Slime molds will eventually go away on their own. When I went back to visit the one in my neighbor’s yard a few days after taking the photo, it had already turned brown and dry and was vanishing.

I happened to notice another, different slime mold on a dead tree in the woods on the Superior Hiking Trail a few days after spotting the one in my neighborhood. Again, I’m no slime mold expert, but I think the one I saw was a false puffball, Enteridium lycoperdon. It was growing on a dead tree. It looked like a big, smooth insect egg sac and was squishy to the touch, like a plastic sack full of dough. Really cool to get to see this!

If you’ve got a slime mold in your yard and you’re not delighted to see it, you can dig or rake it out, but it’ll probably come back when the weather conditions are right. If, on the other hand, you’re thrilled to get a look at this weird being and watch it change color and shape, you can actually grow a bit of it indoors. A number of web sites, such as konnecthq.com/grow-slime-mold, offer instructions on setting up a slime mold science experiment at home.

Written by U of M Extension Master Gardeners in St. Louis County. Send questions to features@duluthnews.com.