Fungus in the Worm Bin - Molds, Mycelium, and Mushrooms

Fungus plays a big role in decomposition, especially for organic materials that are difficult to break down, which will make it easier for your composting worms to eat it later.

Since decomposition is a goal, we want and need fungus in our bin.

Fortunately, fungus is going to find it's way into your worm bin one way or the other..

Most of the time the fungus does it's decomposing work microscopically, but on occasion it can grow enough to become visible to the naked eye - at which point it may dethrone the worms as the dominant species in the worm bin.

So although fungus is beneficial, which I think is the case in most situations, but there are times when excess fungus can indicate harmful conditions in the bin and health of the composting worms.

Let's start with mycelium. Mycelium is the underground network of fungi. It looks like thin, white threads weaving through your bedding and food.

Mycelium only grow in aerobic conditions, so it does indicate healthy conditions in the worm bin, as well as a healthy or well established microbiome.

If you see mycelium growing you should just let it continue to do its thing - as long as its not overwhelming the worm bin. Remember, our goal is to grow worms, not mycelium!

Note that the mycelium you see is not mycorrhizal fungi. Mycorrhizae can only survive by forming a symbiotic relationship with plant roots - they exchange nutrients directly with living plants. 

Unless your worm bin has living plants in it (and even then the odds would be pretty low), mycorrhizal fungi can’t establish there.

The "saprophytic" fungi you see in your bin, although they don't form a direct relation with plant roots, still can help with some of the main benefits to plants that mycorrhizae do.

Technically, I should cover mushrooms in the same portion as the mycelium, as mushrooms are just the reproductive structure of the mycelium.

To compare mushrooms to an apple tree, the mycelium network is the actual live organism, like the tree, while the mushroom is just the apple.

So if you see mushrooms growing in your worm bin, it means that there is mycelium that feel its time to reproduce!

Let the mushrooms run their course. They grow and drop their spores fairly quickly so it shouldn't be much bother to you. Those spores will then grow into more fungus and improve the biome in your bin.

The most common kind of mushroom in the worm bin are inky caps. They are easily identified as their caps will essentially "self destruct" by turning into inky goop. This happens fairly quickly, one day they will be there, and the next they will be gone!

And yes, you can use their inky goop to write and make art with!

Note that any mushroom is safe to touch, but no mushroom is safe to eat unless you have absolutely positively identified it as an edible species (Don't use AI!).

Mold is also fungi, but it does not produce mushrooms, and tends to be "fuzzier" and patchy. It tends to appear on high nutrition foods like bread or fruit. 

Molds generally indicate less than ideal conditions, which could be low oxygen conditions, low pH such as fermentation, or overfeeding.

In my personal experience, seeing lots of mold growth seems to indicate an "immature" or underdeveloped microbiome in the bin (or at least just in the are where the mold is).

Some molds, like Trichoderma and Penicillium, will turn a bright green or blue green. So if your mold is changing colors, it's likely one of those two.

If you see mold, things will probably be okay, but do a general health check up on the worm's health and feel free to break up the mold physically with your hands or some tool.

Every once in a while, you might spot something that looks more like bright yellow goo than fuzzy white growth. It is likely slime mold, and it’s also harmless.

Also called Dog Vomit Mold, slime mold isn’t actually a mold or fungus, rather its a protist. It’s a different kind of organism that feeds on bacteria and decaying matter. 

Slime mold indicates the same things as actual mold - an abundance of nutrients that the worms are leaving available. It won't harm the worms long term, and it's kind of fun to watch it grow, so you can leave it be or break it up.