Nematodes and beetles eat slime mold. Both live in the same damp mulch your blob grows on, and both feed on the plasmodium, which makes them the slime mold predators your yard almost certainly already has. The National Park Service names those two. Your blob is food and a feeder at the same time, so the honest answer runs in two directions at once.
Your mulch bed runs a full food web without your help. Bacteria work on the wet wood chips, the slime mold grazes the bacteria, and nematodes and beetles hunt the slime mold. Your blob sits in the middle of that chain, not on top of it. You notice the blob because the plasmodium spreads out on top of your mulch. In feeding terms you are looking at a mid-level grazer with plenty above it.
Slime molds feed by engulfing. The plasmodium flows over a bacterium, wraps around the cell and pulls the whole thing inside to digest, the same way an amoeba does. That one habit is what separates slime molds from fungi. A fungus absorbs food through its cell walls and never takes a particle in. So the blob on your mulch swallows, while the mushroom you see beside it soaks.
Scale makes the whole thing stranger. A plasmodial slime mold is one enormous cell carrying thousands of nuclei, built when swarming flagellated cells find each other and fuse. A nematode grazing across that sheet is not working through a colony of separate organisms. That worm is feeding on a single cell, one big enough for you to spot from standing height.
- Nematodes, the microscopic worms already living in your damp mulch.
- Beetles, which share that same wet layer and graze on the plasmodium.
- Bacteria feeding on decomposing plant matter, which carry most of the diet.
- Fungal spores your blob flows over and takes inside the cell.
- Possibly smaller protozoa, though that part is less settled.
The prey list stays short, and it stays microscopic. Bacteria feeding on decomposing plant matter carry most of the load, with fungal spores and maybe a few protozoa filling out the rest. Slime molds are saprophytic, so they live off dead material and leave your plants alone. That is the whole slime mold food web in a single bed. Wood chips, then bacteria, then blob, then nematodes and beetles.
A slime mold on your mulch tells you the bed is wet and staying wet, since that is where the plasmodium does best. Rake your mulch open so the surface dries out between waterings.
Read the sighting as information, not as a problem. Predators and prey stacked in the same scoop of mulch mean your decomposition layer is doing the job you spread mulch for. Bacteria are breaking down your wood chips, and something is eating the thing that eats the bacteria. Your bed is working, and your plants pay nothing for the show.
If your blob bothers you, break the crust apart with a rake. Skip the fungicide. A slime mold is not a fungus, so your spray has no real target. Damp conditions brought your blob in, and drier conditions will send the same blob away again.
What slime molds eat is a short list. Bacteria, fungal spores and perhaps a few protozoa, and nothing you planted. Nematodes and beetles handle the other side of that trade. Both halves happen in the top layer of your mulch, out of your sight until the plasmodium spreads wide enough to catch your eye. Your slime mold predators are already at work, and your bed sorts the rest out without you.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
