Most nematodes in your soil are not pests. They are microscopic roundworms grazing bacteria, pruning fungi, and hunting each other — and the vast majority are on your side. The plant-parasitic kind (root-knot and friends) get all the press; this page is about the good ones.
The three beneficial types
Bacterial-feeding nematodes graze bacteria like cattle. Like protozoa, they excrete excess nitrogen in plant-available form as they eat. They are the most numerous nematodes in healthy soil.
Fungal-feeding nematodes pierce fungal threads with a hollow spear called a stylet and drink. In moderation they prune fungi and cycle nutrients; in excess they can stress mycorrhizae. Balance, as always, is the whole game.
Predatory nematodes are bigger nematodes that hunt smaller ones — including the root-feeding species gardeners worry about. A diverse nematode community polices itself, which is one more reason not to nuke the soil.
Not to be confused with: the bad guys
Root-knot and other plant-parasitic nematodes attack roots directly and cause galls, stunting, and yellowing. If that is your problem, see our nematode pest guide — different worms, different war. The beneficials here are the ones you want more of, not fewer.
The ones you can buy
Some beneficial nematodes are sold as biological control: Steinernema species for mole crickets and fire ants, Heterorhabditis bacteriophora for grubs. They work when applied to moist soil in warm weather — microscopic worms hunting underground, exactly like their wild cousins. Our IPM guide calls them a genuinely useful Florida tool.
How to keep them
- Keep soil alive. Nematodes need bacteria, fungi, and each other — which means organic matter and mulch, not bare dirt.
- Don’t fumigate. Anything that kills all nematodes kills the police force too.
- Stay moist. Nematodes live in water films. Dust-dry soil is a desert to them.
Meet the rest of the underground workforce in the Soil Food Web Explorer.
🌱 Keep learning
Three related guides worth reading next:
- Living Soil — A field guide to everything alive in your dirt: bacteria, fungi, protozoa, nematodes, worms, and the whole food web.
- Soil Microbiology — Meet the billions of microbes doing the real work under your feet.
- Organic Matter: The Pantry — The pantry the entire soil food web eats from — fallen leaves, dead roots, compost, and why it matters more than any fertilizer bag.