They’re creepy and crawly, but are worms harmful to your landscape? There’s a general rule of thumb to help you tell the good worms from the bad.
Slimy worms? Yes. Destructive? Maybe.
There are two categories of worms that you might find in your lawn, garden, or flowerbeds. One is a genuine worm, the earthworm or “nightcrawler.” (Although nematodes are a different species, they can also be included in this group.) The second category includes juvenile insects and caterpillars. These are the precursors to beetles, moths, or other insects in their early stages of development.
The general rule regarding which worms are helpful and which are hurtful is that legless earthworms and some nematodes are beneficial in the landscape. At the same time, any worm that crawls on its legs (like a caterpillar) is usually destructive.
They only come out at night.
Earthworms are often called the farmer’s friends because of the nutrients they contribute to plant life. They stay under the soil except to emerge on the surface at night, thus the nightcrawler label. Earthworms eat organic waste, dead things, nematodes, protozoa, and residue in the soil. Their excrement, called “castings,” enriches the soil, feeding plants. Many gardeners buy earthworms or fertilizer with castings for their gardens.
Nematodes serve a different role in landscaping and must be the right kind to be helpful. There are 20,000 known species of nematodes. Some nematodes, such as pinworms, roundworms, and hookworms, cause parasitic sickness in animals and humans.
Beneficial nematodes, called entomopathogenic nematodes, live in the soil and are microscopic. They feed on caterpillars and soil-borne insects, thus acting as a natural insecticide. They are not parasitic to animals or humans.
Thus, good nematodes can help deal with the other bad category of worms in the landscape: caterpillars and other destructive insects.
What’s eating the leaves on your garden plants?
At some point, every gardener finds holes eaten all over the leaves of their plants. It’s disheartening to see your beautiful broccoli chewed to pieces and find a bright-green caterpillar doing its dastardly damage on the underside of the leaves.
Once such caterpillars are on the foliage, spray treatments or manually finding and squishing them are your only options. Nematodes can kill them when they are in or on the soil, but not once they’re on the leaf canopy.
Related – Creepy Crawlies and Critters Can Damage Your Yard