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Earthworms

Also known as Red wiggler (Eisenia fetida), Nightcrawler (Lumbricus terrestris)

Beneficial or harmlessDepends
A common garden earthworm, Lumbricus terrestris Photo: Donald Hobern from Copenhagen, Denmark · CC BY 2.0

In short

Earthworms are among the most valuable animals in garden soil: their burrows aerate and drain it, and their casts enrich it. In a pot the picture changes. There is little for them to eat and little room, so a worm that has crept in through a drainage hole is better moved to the garden.

How it looks

Soft, segmented, legless tube-shaped bodies, usually reddish to brown, from about 1 cm long in small species to roughly 36 cm in the nightcrawler (Lumbricus terrestris). Adults have a thickened band, the clitellum, part-way along the body. Compost worms such as the red wiggler (Eisenia fetida) live in leaf litter and compost; others burrow sideways in the topsoil or make deep vertical burrows. Eggs are laid in small lemon-shaped cocoons.

Signs

In the garden: small heaps of worm casts on the surface and a crumbly, well-drained soil. In pots: worms rising to the surface after heavy watering, casts around or under the drainage holes, or worms seen through the holes.

Life cycle

Earthworms are hermaphrodites that exchange sperm; fertilised eggs develop in cocoons left in the soil, and between 2 and 20 young hatch from a cocoon after about three weeks.

What favours it

Moist soil rich in organic matter. They need moisture to keep their skin damp. Pots stood on bare soil or lawn are easily colonised through the drainage holes.

Prevention

  • Stand outdoor pots on feet, gravel or paving rather than directly on soil.
  • Use bagged potting mix rather than garden soil for container plants.
  • Check new plants from outdoor nurseries at the drainage holes when you bring them home.

Treatment

Start with the first step and move down only if the problem persists.

  1. In the garden, no action: encourage them with mulch and organic matter.
  2. In a pot, soak the whole pot in a bucket of cool water until the mix is saturated, then lift it out; worms tend to come to the surface and can be picked off and released in the garden.
  3. Alternatively, slide the root ball out of the pot and pick worms off by hand before repotting.

Pros and cons

Pros

  • Burrows create channels that improve aeration and drainage.
  • Mix organic matter into soil and speed nutrient cycling.
  • Casts are rich in humus; vermicompost made by red wigglers is a useful soil amendment.

Cons

  • In a small pot there is little decaying matter for them to eat, and a hungry worm may disturb or nibble roots.
  • Garden earthworms such as nightcrawlers need cooler, deeper soil than a pot can give and do not thrive in one.

Look-alikes

Fungus gnat larvae
Much smaller (a few millimetres), translucent, with a shiny black head.
Millipedes
Millipedes have a hard, segmented body and many legs; worms have no legs.

Where you find it

Beneficial in garden beds, lawns and compost. Unwanted in most containers and houseplants.

Sources

  1. Earthworm — Wikipedia
  2. Vermicomposting Puts Worms to Work — Penn State Extension
  3. How to Get Rid of Worms in Houseplants — Hunker

Written in our own words from these sources. Check a product label before using any treatment.