Slime molds are no garden threat

Friday, August 28, 2015

BY KENNETH SETZER
As published in the Miami Herald, 8/28/15.

Ever wander outside to find what looks like a shredded kitchen sponge — an alarming, shocking, bile yellow — roiling its way over your mulch? Is it an animal, plant, fungus or maybe some unholy combination? You may be cohabitating with slime mold.

 
Fuligo septica, dog vomit slime mold

It can also look a bit like scrambled eggs or the partially digested matter dogs like to vomit. “Fungus” might immediately pop into your worried mind, but this isn’t a fungus at all. What you have is Fuligo septica, the aptly named dog vomit slime mold. Slime molds are weirder than you think.

 
Fuligo septica as it ages and produces spores

Slime molds are not molds (which are in the fungus kingdom) but rather fall into the kingdom Protista, one of the stranger of the six or so kingdoms of life. The vomit slime mold — let’s call it Fuligo — is the one you are most likely to notice, especially on mulch. Many other slime molds are quite small, but you might see them on very damp, well-decayed wood.

 
Stemonitis sp., common slime mold on rotting wood

If slime mold spores successfully germinate, they can come together to form what’s called the plasmodium. Sources describe it as a giant cell composed of many nuclei (there is another type of slime mold). The plasmodium does indeed creep and crawl in search of food. If all goes well, it will produce its fruiting bodies and spores, and the process will continue.

 
Lycogala epidendrum, wolf’s milk slime mold

I find it tough to get my mind around its means of existence and reproduction. Slime molds seem just so biologically alien from what we are. But that’s my anthropocentric prejudice. The main point for us to remember is that slime molds are harmless to animals and plants. Fuligo in particular is innocuous and even eaten by people in some parts of the world.

Like us, slime molds first ingest, then digest their food. Fungi on the other hand break down their food by secreting enzymes before absorbing the available nutrients. And of course, plants do away with all this nasty business by making their own food.

The bright yellow Fuligo fades into a pinkish beige once the spores begin to form into a mass called an aethalium. The entire Fuligo will now dry out and harden. It soon releases its spores as a brown powder, and begins to decay and disappear until conditions are right for the next generation.

Though many unknowns still exist, slime molds have been studied extensively. They have been shown to be able to find food in a maze and react to stimuli like light. In some, the many individual cells can exist independently and signal each other at the right time to come together and behave like a single colony, some having different roles in the community, all while moving around like a single creature. Some have even been chopped up in the lab, only to find each other and reunite!

Another slime mold you may have seen is wolf’s milk (Lycogala epidendrum), often found on soil and mulch. Before aging, it lives as small globes of bright bubblegum pink, fading to beige. One of the most common slime molds, often mistakenly identified as a fungus, is Stemonitis, a genus sometimes called chocolate tube slime. It looks like a mass of brown wires.

If you find any of these slime molds, be sure to look at them up close, preferably with a hand lens, and you will be amazed by their minute, intricate beauty. I’ve read they can even be brought home and kept alive eating oats. Though, outdoors, they prefer eating bacteria, fungi, and other microorganisms — but not plants.