Types of Worms in Soil — 7 You Find and What Each Does

Dig a spadeful of damp garden soil and you will turn up several animals that all get called worms. Most are earthworms doing three completely different jobs, one is a problem, and several are not worms at all.

The three earthworm groups

Ecologists sort earthworms by where they live rather than by species, and it predicts what they do to your soil better than any name does.

1. Red wiggler — Eisenia fetida (epigeic). Red-brown with pale banding, 2–4 in, and the species in almost every wormery sold. It lives in decomposing organic matter rather than soil, so it will not establish in a garden bed. Finding it in a compost heap is the sign the heap is working.

2. Grey worm — Aporrectodea caliginosa (endogeic). Pale grey-pink, unremarkable to look at, and probably the most abundant worm in cultivated soil across temperate gardens. It spends its life eating its way horizontally through the top few inches, which is the mixing that makes topsoil topsoil.

3. Nightcrawler — Lumbricus terrestris (anecic). The big one, 4–10 in, dark red at the head and paler toward the tail. It holds a single permanent burrow that can run several feet down, comes to the surface at night to pull leaves in, and leaves casts at the entrance. Those burrows are the reason worm-rich soil drains after heavy rain.

4. Jumping worm — Amynthas species (epigeic, invasive). Also sold as snake worms or Alabama jumpers. They strip the leaf litter layer in a single season and leave behind a loose, granular soil with the texture of coffee grounds that holds neither water nor seedlings well.

The things that are not earthworms

5. Pot worms — Enchytraeidae. White, thread-thin, under half an inch, often in hundreds in a wet compost heap or a saturated pot. Harmless decomposers. They are not baby earthworms — those hatch already pigmented — and a population explosion is a reading on wet, acidic, organic-rich conditions.

6. Wireworms — click beetle larvae. Hard, shiny, orange-brown, stiff, about an inch, with three pairs of legs behind a distinct head. They bore into potatoes, carrots and the stems of young plants, and they are commonest in ground that was grass within the last three years.

7. Cutworms — moth larvae. Fat, grey-brown, soft, and curled into a C when disturbed. They sit just below the surface and cut seedlings off at soil level overnight, which is a symptom no earthworm ever causes.

Telling them apart in the hand

The distinction that matters is worm against larva, and three features settle it every time.

• Legs. Any sign of them means an insect larva. Earthworms have none.
• Head. A larva has a hard, darker head capsule. An earthworm’s front end is the same soft tissue as the rest of it.
• Segments. An earthworm is ringed evenly from end to end. A larva has a few obvious body divisions rather than dozens.

A mature earthworm also carries a clitellum, the smooth swollen band about a third of the way back. Its colour and position is what separates a jumping worm from a nightcrawler, and it is the single most useful thing to look at.

What the count tells you

Ten or more earthworms in a spade-depth hole of damp spring soil is a reasonable population for a productive bed. None at all, in soil that is moist and not frozen, points at compaction, very low organic matter, or recent heavy cultivation rather than at anything you need to add.

The way to raise the number is to feed them: surface mulch, compost, and leaving the soil alone. Buying worms does not work, because the species on sale are the one group that does not live in soil.