Are Earthworms Good For Gardens?

  What Are Earthworms?


The term Earthworm refers to a specific group of invertebrates within the taxonomic phylum Annelida. Earthworms belong to the Oligochaetes — which means 'few bristles.' Worldwide there are over 3,000 species described. Earthworms are, as their name suggests, terrestrial, their skin is permeable and they need a moist environment so they don't dry out.

The different species of earthworms have individual requirements just as a dog has from a cat, some earthworm species live in compost, some live in permanent burrows deep down in the soil, others are content with the middle ground and make complex networks of tunnels as they explore the earth.

Read more: The Problem With Earthworms
Read more: YIKES! Invasive Jumping Worms

  Why Aren't There Any Native Earthworms In Wisconsin?

There is no evidence that earthworms ever inhabited Wisconsin before European settlement. Even if they did, the glaciers killed any native North American earthworms in our region. For the last 11,000 years since the glaciers receded, Wisconsin ecosystems developed without earthworms.

  What's the Difference Between Earthworms and Nightcrawlers?

Earthworms and nightcrawlers are terms that are often used interchangeably. In reality, the two worms differ in appearance, function and when and where they are seen. Nightcrawlers, otherwise known as dew worms or garden worms, appear at night when the dew is on the grass or sidewalks.

  Earthworm Anatomy

An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan, are externally segmented with corresponding internal segmentation. To learn more about earthworm anatomy, click the button below.

  Earthworm Reproduction

Earthworm Reproduction Earthworms are hermaphrodites, meaning they have both male and female reproductive organs.

When two earthworms are ready to mate they adopt a head-to-tail position, cover themselves in a layer of mucus, and exchange sperm. The saddle produces a mucous tube which detaches and moves forward along the body, collecting on the way the earthworm’s own eggs and the sperm received from its partner.

Fertilization occurs in the mucous tube which is shed from the front end of the earthworm. This dries in the soil to become an egg capsule, from which one or more young earthworms will eventually hatch. Many species can reproduce several times a year.

  How Do Earthworms Benefit The Garden?

  Soil Formation

Earthworm Soil Formation Graphic We all know that a healthy compost heap is writhing with worms, working their way through the kitchen and garden waste to help create organic matter to feed our soil—these are mostly brandling worms, recognized by their red, stripy appearance—but I’m talking about the worms which, if your soil is good, you’ll find in large numbers throughout your vegetable plot. How useful are they?

Well, first, they’ll be munching on leaf fragments and other plant debris that accumulate on the soil surface. Research indicates that, having passed through worms, these bits and pieces are broken down more easily by microbes. Result? Humus! That black gold beloved of all organic gardeners is produced more quickly with the help of worms than by microbes alone.

Read More: What Is Soil?

  Soil Structure

Earthworms play a key role in modifying the physical structure of soils by producing new aggregates and pores, which improves soil tilth, aeration, infiltration, and drainage. Earthworms produce binding agents responsible for the formation of water-stable macro-aggregates.

Read More: The Basics of Soil Aggregation

  Nutrient Cycling

With worms having little to do but eat, they shift a surprising amount of material. One study on forests came to the conclusion that worms buried over 90% of the plant debris left on the soil surface. Another indicated that an impressive forty tons of soil per hectare were brought to the surface in worm casts in the course of a year.

This is great news as worm casts tend to be very fertile, holding more calcium, iron and phosphorous than the soil around them. They also contain significant amounts of nitrogen and help to stabilize carbon, reducing the release of carbon dioxide from the soil. The small particle size in the casts means they can even hold more water.

  Water Absorption

Of course, worms also burrow, and not all in the same direction. Epigeic species burrow in the litter on the soil surface; Anecic species live in vertical burrows that can descend several feet. Endogeic species burrow below the surface in horizontal or random lines. Aristotle described worms as "the intestines of the soil", which is a good way to regard the passages they create. Burrows open up the soil to air, bringing oxygen to plant roots, and create pathways for water and roots. The presence of earthworms has been shown to have a notable effect on the amount of water a soil can hold and on how fast it sinks in.

  Red Wrigglers — Composting Favorite

Red Wrigglers, Eisenia foetida, held in a hand

Red Wrigglers are earthworms too and they have many properties which make them ideal for the compost bin. Of all the worms suitable for composting, the Red Wriggler is the most adaptable and hearty. They can withstand a wide range of environmental conditions and changes that would kill most other earthworms. The Red Wriggler's voracious appetite makes it the champion of the compost bin and a virtual worm casting (worm poop) machine.

Red Wrigglers are fairly small, generally getting no larger than 5 inches. They like to live in colonies, often congregating into a writhing mass around a food source. Maintaining this close contact makes them prolific breeders.

They can withstand a wide range of temperature extremes. Typically Red Wigglers thrive in temperatures between 65° F and 80° F. When the temperature dips, Red Wrigglers need to be protected from freezing weather.

Read More: Vermiculture Basics

  There Are 3 Groups Of Earthworms

There are thousands of earthworm species worldwide. These species are placed into one of three groups based on their feeding and burrowing habits. Each group contributes to soil health in different ways, but they all have a couple of things in common.

  Epigeic Group

Earthworm types Epigeic, Endogeic and Anecic graphic This group is composed of species that primarily consume plant litter and organic matter at the soil surface and make nutrients more rapidly available for plant uptake. Epigeics are small worms with short life spans (3 to 4 years) and high reproductive rates. During winter, they bury themselves under the litter layer to survive, but if the top foot of soil freezes, they die.

  Endogeic Group

Members of this group create continuous horizontal burrows within the soil profile and feed on subsurface soil enriched with organic matter. These earthworms help aerate the soil as they burrow. Endogeics have lower reproductive rates than epigeics, are larger, and have longer life spans (up to 6 years). In winter, they burrow deeply in the ground and fall into a dormant state.

  Anecic Group

This group of earthworms, which feed on surface litter and create deep vertical burrows, incorporates organic material into the mineral portion of the soil (below the surface) by pulling surface litter into their burrows. The vertical burrows also improve water flow through the soil. Anecics have the lowest reproductive rate but are the largest earthworms with the longest life span (4 to 10 years). They retreat deeper into the soil and go dormant when cold temperatures arrive.

  Did You Know?

  There are over 100 known native earthworm species in the United States. They primarily reside in undisturbed native habitats (forests and grasslands) that were not glaciated.
  Exotic earthworm species were accidentally brought over on colonial ship ballasts and in potted plants during the 1700s through the 1940s. They thrive in and dominate large stretches of land that have been disturbed (agricultural and urban areas).
  Earthworms can process around 0.08 to 0.3 grams of soil in one day, depending on the species.
  Earthworms are hermaphrodites (have both male and female reproductive organs). When two earthworms mate, both transfer sperm to one another and grow egg cocoons in the clitellum (the engorged region close to the middle of a mature earthworm).
  Earthworm eggs hatch in about 3 weeks under favorable soil conditions.
  Earthworms can live from three to ten years, depending on the species and soil conditions.

  Looking After Worms

Earthworm Cartoon Given their activities, it’s a good idea to encourage as many as possible to hang out in your soil, so my first suggestion is to dump the rototiller. Agricultural research has shown that the more soil is tilled, the fewer the worms are in it and, despite rumors to the contrary, worms cut in half do not grow into two worms. It’s true that, in some circumstances, one half might survive, but on the whole you can assume that a bisected worm is a dead worm.

Digging also presents a clear and present danger to them, though on nothing like the scale of a rototiller, and worm safety is one of the reasons I’m a great advocate of No-Dig beds which leave soil undisturbed. If you must dig, using a garden fork rather than a spade is less likely to damage worms.

Bear in mind, too, that worms eat organic matter and, if supplies drop off, they will vote with their contractile tissue and move elsewhere. They also need moisture, which is why in dry weather you’re likely to find them in the damp soil under stones or wound into a tight ball. It’s their way of protecting themselves from heat and dryness until conditions improve.

The best answer to keeping worms happy is to look after your soil.

Ensure that it’s well fed with compost and spread with mulch, and don’t dig unless you have to. Not only will it be good for your plants, but the organic matter and improved water retention will make the worms want to call your garden home.

Further Reading:

 Take The Earthworm Quiz
 Are Earthworms Truly Good For Your Garden?
 YIKES! Invasive Jumping Worms
 Soil Biology
 Native Plant Root Systems

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