Earthworms in Your Garden: Good or Bad?

“Worms have played a more important part in the history of the world than most persons would at first suppose.” - Charles Darwin

Unless you are an avid gardener, you most likely aren’t even aware of what is going on in the soil, preferring only to notice how well the grass is doing or what flower is blooming, and that is just fine! But there, one soil-dwelling organism is dutifully toiling away; burrowing and recycling organic matter right under your feet!

Many of us were raised to respect and appreciate the unsung hard work of these wriggling little slimy beings, grateful to them for enriching the soil. Always saving one when it gets caught on the sidewalk after a rain.

Earthworm Basics Types of Native Earthworms

Worm Intelligence?
Beneficial Superheros or Invasive Pests?
Encouraging Native Earthworms
Earthworms Are Here To Stay!

Earthworm Basics

There could be up to 200 Earthworms per square meter of topsoil, burrowing and eating dead leaves and roots. Happily doing their thing oblivious to the rigors of our modern world. These invertebrates live anywhere in the world where there is ample food, moisture, oxygen, and favorable temperatures.

There are more than 2,500 species of Earthworms throughout the world
Earthworms have the ability to regenerate or replicate lost segments
Earthworms' bodies are made up of ringlike segments called annuli
Baby worms hatch from cocoons smaller than a grain of rice
Move and burrow using small bristles called setae
Have simple nervous systems (brain) which is a cord that runs the length of their body
They have 5 ‘hearts‘ - also known as aortic arches along their entire body
The three main parts of an Earthworm are:

The head segment
The saddle (clitellum) - a fleshy ring like the collar of a turtleneck sweater
And the tail

Worms are cold-blooded invertebrates
If a worm’s skin dries out, it will die
Worms are hermaphrodites

Earthworms are essentially one long digestive system, an outer muscular body wall surrounding a digestive tract that begins with the mouth in the first segment.

They are usually considered beneficial organisms, vital to soil health by transporting nutrients and minerals to the surface by way of their waste - called castings.

The slimy secretion on the outside of an Earthworm contains nitrogen, which is an important nutrient for plants and helps hold soil particles together. Earthworm mucus helps them glide through the soil and it helps them breathe through their skin. This is why they, and their environment, must be moist at all times.

More Earthworm Facts

The largest U.S. Earthworm native to the Pacific Northwest grows up to 3 feet!
In one acre of land, there can be more than a million Earthworms!
The largest Earthworm ever found was in South Africa - measuring 22 feet!
The Australian Gippsland Earthworm grows 12 feet long and weighs 1-1/2 pounds.
Worms can eat a third to 100% of their weight a day
They can push ten times their own body weight.
Baby Earthworms can push five hundred times their own body weight
One Earthworm can digest 36 tons of soil per year!
The common Earthworm can live up to 6 years
They are food sources for birds, toads, and many mammals and rodents

Types of Native Earthworms

There are over 100 species of native Earthworms in the Southeastern U.S. and the Pacific Northwest. Oddly enough - nearly every Earthworm in the Northern U.S. actually came from somewhere else!

Native Earthworms north of Pennsylvania all but disappeared more than 10,000 years ago, when ice age glaciers wiped them out.

Kentucky Earthworm (Komarekionidae)
Mud-Dwelling (Sparganophilus)
(Megascolecidae) 76 species native to North America
Diplocardia Earthworms along the Pacific Coast
Driloleirus macelfreshi - Largest Earthworm in the Pacific Northwest, grows up to 3 feet
Louisiana Mud Worm (Lutodrilus multivesiculatus) is semiaquatic and found only in Louisiana in mud flats and swampy areas.

Non-Native Earthworms

The non-native Earthworms first arrived with soil and plants brought from Europe, most likely in ships traveling to North America which used rocks and soil as ballast, which was then dumped on shore as early as the 1600s. European plants likely had worms or their cocoons in the soil too.

Today, the use of Earthworms as fishing bait has spread them further! All common bait worms are non-native species, including those sold as Night Crawlers, Canadian Crawlers, Leaf worms, or Angle worms. At least fifteen non-native species have been introduced so far.

Lumbricus rubellus - The familiar Red Worm can trace its origins back to the Old World. Common in coniferous forests of its native Europe. Of the 33 species, many have become naturalized throughout the world.
Megascolecidae and Asian Pheretimoid Earthworms, also known as Jumping Earthworms, Snake worms, Alabama jumpers, and Crazy Snake worms, are starting to spread in the Great Lakes states. These worms squirm violently like snakes and act very differently from other worms. Not as slimy, they have a different colored, pronounced saddle. Jumping Worms outcompete their European competitors by consuming food faster, stripping the forest floor of organic matter, and reproducing rapidly, displacing the local populations. They also seem nearly impossible to eradicate.
Eisenia fetida - known as Manure worm, Redworm, Brandling worm, Panfish worm, Trout worm, Tiger worm, and Red Wiggler Worm. These non-natives are sold and shipped all over the country for home compost piles and vermicomposting (worm composting). The most common type of invasive worms, Red wigglers are about an inch in length and have a reddish-brown color. Discovered to possibly be harming plants through their natural feeding habits, they are possibly toxic to creatures that naturally eat Earthworms such as garter snakes, frogs, and turtles.

Worm Intelligence?

How can something with no eyes, limbs, ears, or an obvious brain be smart you ask?

Even without eyes, they can sense light and move away from it, becoming paralyzed if exposed to as little as 1 hour of light.

Charles Darwin spent 39 years studying Earthworms, suspecting they had basic intelligence. After watching them choose leaves by their shape, he learned that Earthworms pulled food into their burrows by the ends most likely to fit.

We used to think Earthworms raced onto the pavement during rainstorms to avoid drowning but now theories suggest that they’re actually confusing the sound of raindrops with moles digging through the soil. They can feel sound vibrations and avoid underground predators such as moles, other mammals, and snakes. Other experiments show they can learn to navigate mazes and get faster each time. If threatened, Earthworms ‘herd’ together, and communicate by touch.

This makes me feel even worse whenever I jab one on a fishing hook!

Beneficial Superheros or Invasive Pests?

While most of us know Earthworms are beneficial creatures that work away at enriching the soil, there is a realization that they may not be without their faults too.

The Good News

Where they are native and when in the vegetable garden setting, aerating and loosening soil, Earthworms are very beneficial! They create and enrich the soil, loosen soil compaction, and their tunnels create "macro-pores" that help water move through the soil. They also help incorporate organic matter and minerals into the soil to make more nutrients available to plants.

As Earthworms chew and churn the soil, researchers suspect they have an impact on its ability to store that carbon, easing many of our climate change concerns. As organic material decays, it releases CO2 into the atmosphere, and Earthworms both help speed up the process as they break down leaf litter and wood, causing microbes to release more CO2 than normal, they also excrete soil as casts which take longer to break down, making it so the carbon stored there stays in the ground longer.

Encouraging Native Earthworms

Don’t till or disturb the soil
Organic fertilizers and composts
Increase organic matter in the soil
Make a compost heap in the backyard

The Bad News

Because Earthworms weren’t around since the ice age, Northern hardwood forests developed in their absence by relying on the microbial and bacterial decomposition of the leaf litter - which is slow and steady. Creating a spongy layer of organic "duff", which is a deep, natural environment for native woodland wildflowers and understory shrubs.

Earthworms moving in from other parts of the world, or up from the Southern US and South America, break down leaf litter too fast - changing forest soils and robbing plants of organic nutrients. Reducing the variety of understory wildflowers and shrubs and inhibiting tree seedling growth. There is also less duff soil habitat for ground-dwelling animals. This loss of duff is also increasing soil erosion. These same issues are arising in home landscapes and agriculture as well.

Earthworms Are Here To Stay!

So are they good or are they bad? It’s up to you and where you live, but these curious little (and not so little) ground-dwelling invertebrates are here to stay! So we might as well embrace them for the good they can do when in the right location.

We’d love to hear your thoughts on these unique creatures! So join us on the Nature Hills YouTube, our #ProPlantTips Garden Blog, or on one of our many social media sites to hear your thoughts!

Happy Planting!

Frequently Asked Questions

Are earthworms actually good for your garden soil and plants?

Yes, earthworms are highly beneficial to garden soil and plants. They transport nutrients and minerals to the surface through their waste castings, and their mucus secretions contain nitrogen, an important plant nutrient that also helps bind soil particles together. With up to 200 earthworms per square meter of healthy topsoil, their burrowing activity also improves drainage and aeration. To encourage a thriving earthworm population, avoid tilling excessively, reduce chemical inputs, and add organic matter like compost to give them a steady food source.

Can earthworms ever damage or hurt your plants?

Earthworms are generally beneficial to plants and soil health, but in very high concentrations they can disturb shallow root systems and disrupt the natural leaf litter layer that many native plants depend on for nutrients. Invasive European earthworm species in particular have been documented causing harm in northern hardwood forests by breaking down organic matter too quickly for native ecosystems to adapt. If you notice excessive worm activity around sensitive plantings, improve drainage in those areas and avoid over-mulching, which creates ideal conditions for population explosions.

Why are earthworms considered beneficial for the environment?

Earthworms are considered beneficial because they continuously transport nutrients and minerals to the surface through their waste, known as castings, which directly enrich the soil for plant growth. Their slimy secretion contains nitrogen, an essential plant nutrient, and helps bind soil particles together for better structure. With up to 200 earthworms per square meter of topsoil, their collective burrowing also improves drainage and aeration throughout your garden beds. To encourage their activity, maintain consistent soil moisture, add organic matter like compost or mulched leaves, and avoid chemical pesticides that can harm or kill worm populations.

How do earthworms improve soil health in a home garden?

Earthworms improve soil health by burrowing through the ground and breaking down dead leaves and roots, then depositing nutrient-rich waste called castings that deliver essential minerals directly to plant roots. Their mucus secretions contain nitrogen, a key plant nutrient, and help bind soil particles together for better structure and drainage. To encourage earthworm activity in your home garden, maintain consistent moisture, add organic matter like compost or leaf mulch, and avoid tilling or using chemical pesticides that disrupt their populations.

Should you be concerned if you find a lot of earthworms in your garden beds?

Finding a lot of earthworms in your garden beds is generally a positive sign, as populations of up to 200 worms per square meter indicate rich, healthy soil with plenty of organic matter, moisture, and oxygen. However, if you are in a northern forested region, it is worth identifying whether the worms are native species or invasive European varieties, which can disrupt natural forest ecosystems. For most home gardeners, a thriving worm population means your soil is in good shape, so focus on maintaining that balance by adding compost, avoiding compaction, and minimizing tilling to keep your worm community healthy and productive.

Can earthworms cause any problems in certain garden situations?

Yes, while earthworms are generally beneficial, non-native invasive species can cause serious problems, particularly in northern forest gardens and naturalized woodland areas where they can rapidly consume the organic duff layer that native wildflowers and tree seedlings depend on. In established garden beds, extremely high worm populations can occasionally over-aerate or disrupt the root zones of delicate plants. To keep earthworm activity in balance, avoid over-mulching with thick layers of organic material that can attract populations beyond what your soil ecosystem can support, and focus on planting native species adapted to your local soil conditions.

How do earthworms help or hurt plant roots specifically?

Earthworms benefit plant roots by loosening compacted soil through their burrowing, which improves drainage and allows roots to penetrate deeper and access more nutrients. Their castings deposit nitrogen and minerals directly into the soil, feeding root systems naturally and improving soil structure around existing roots. However, certain invasive earthworm species, particularly jumping worms, can devastate root systems by consuming the organic layer that protects shallow-rooted plants. To support healthy root development, focus on building organic matter through mulching and composting, which encourages native earthworm populations while giving plant roots the nutrient-rich environment they need to thrive.

Are earthworms safe to handle, and can they harm you?

Earthworms are completely safe to handle and pose no threat to humans whatsoever. They have no teeth, no stingers, and no venom, and their only defense is a slimy mucus coating that helps them move and breathe through their skin. That mucus does contain nitrogen, which is actually beneficial to plants and soil. Feel free to pick them up with bare hands, and if you find one stranded on a sidewalk after rain, simply return it to moist soil or a garden bed so it can survive.

Should you actively try to attract more earthworms to your garden?

Yes, encouraging earthworms in your garden is generally a smart move, as they aerate soil, transport nutrients, and produce castings that feed your plants naturally. Native earthworm populations thrive when you maintain moist, organic-rich soil and avoid tilling, which disrupts their tunnels and kills them outright. Add a 2 to 3 inch layer of compost or mulch over your beds to give them the food and moisture they need to establish. Skip the chemical fertilizers and pesticides when possible, as these can harm or drive away the worm populations already working in your soil.

How can you tell if your garden soil has a healthy earthworm population?

A healthy earthworm population in garden soil is generally indicated by finding roughly 10 or more earthworms when you dig up one cubic foot of soil. You can perform a simple counts test by digging a hole about 12 inches deep and 12 inches wide, then sifting through the removed soil and counting what you find. Rich, dark, crumbly soil with visible castings on the surface is another strong sign of thriving worm activity. To encourage a healthy population, add organic matter like compost or mulch regularly and avoid chemical pesticides that can harm worm populations.

Earthworms! Good or Bad For The Environment?