The Mysterious Appearance and Disappearance of Dog Vomit Slime Mold

If you clicked on this title and got this far, good for you!

Not too many people would be interested in something as gross-sounding as dog vomit slime mold (Fuligo septica), but here you are. Congratulations! 🙂

This past week here at the homestead we had an eruption of yellow masses in our front mulch bed. They seemed to appear out of nowhere, grow quickly, and then fade away within 24 to 48 hours. Intrigued, of course, I took some pictures and did a little research to find out what was going on. Turns out these yellow masses of goo are slime molds. Slime molds are not plants or animals or even mold/fungi. They are “simple organisms that consist of a mass of creeping gelatinous protoplasm containing nuclei” or, in other words, amoebas.

“Creeping gelatinous protoplasm” is a good descriptor. When they first appeared in our mulch bed, they were simply oozing, slimy blobs of neon yellow goo coming up through the mulch. And then they grew and spread.

First sign of dog vomit slime mold coming up

Within hours, they transformed into beautiful, intricate, spongy-looking mounds of yellow fluff.

Beautiful color and intricate, spongy pattern on the “blooming” slime mold

The small masses then grew into large bright yellow patches, up to 18 inches across. They seemed to be creeping across the surface of the mulch bed trying to get somewhere.

Dog vomit slime mold at its peak
Check out the size of this patch of slime mold!

By the next morning, the bright yellow was fading into tan and the surface began to look like a crusty slice of toasted bread. This must be the stage that prompted its name – dog vomit slime mold. But it has no smell to speak of and so never bothered us.

24 hours later, fading away…

As they hardened further, cracks formed on the surfaces, and the edges rounded like a pancake cooking.

Slime mold crusted over – about 30 hours after it first appeared

Another day later, the blobs were turning gray, and when I touched the surface, it felt like powder over a crunchy hard shell. The powder is millions of spores, ready to be carried away with the wind.

Two days after it first appeared – fading and powdery – spores ready to be swept away with the wind.
Where I touched the slime mold, you can see the dark substance underneath, some of the yellow surface remnants, and the remaining powdery white/tan spores.

There are more than 900 species of slime molds. This dog vomit slime mold is fairly common and seems to appear most often in mulch beds after a rain in spring. Here are some fun facts about it:

  • The bright yellow mass we see is called the plasmodium and is one huge single cell with multiple nuclei.
  • Slime molds are not harmful and do not cause plant or animal diseases
  • They live on surfaces and do not have the deep-reaching mycellium like some mushrooms do
  • They actually move, as fast as 1 mm per hour
  • They “eat” bacteria by surrounding and engulfing them
  • They take up soluble nutrients from their environment and are amazingly resistant to highly toxic levels of Zinc (They produce a yellow pigment which has been shown to grab and bond to metals and convert them to inactive forms.)

So, check your yard and watch for these cool spring organisms. The name may sound ugly, but they’re pretty fascinating to observe in the gardens!


  1. This taught me something today and made me laugh.
    It made me think back to a post on social media some years ago.

    This slime or something very similar popped up in a suburb/residential area of a nearby city, and a mother noticed it on her property and posted about it on social media. It really surprised and upset a few folks, and it caused quite an uproar within said suburb group. Silliness, truly.
    No one knew what this strange thing was and why it popped up.

    I guess it goes to show, it does not matter how prim/pretty your yard is or is not.
    Nature does what it wants with what is available.

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