Worms from compost in a man's hand.

Why You Need Worms In Your Compost

Worms are truly incredible creatures. There’s also a huge amount of them.

An acre of good soil can contain up to 3 million earthworms, together moving 18 tonnes of soil a year in their search for food and creating 10 to 15 tons of worm castings. (Source: Teaming with Microbes). They are hugely important for the soil, and they also play an important role in the compost – especially during the cooling and maturing phases.  

Worms help us make compost (indeed, vermiculture or worm composting totally relies on worms), while adding compost to the soil encourages other worms which in turn benefit the soil. 


Worms through history

Our appreciation of the value of worms is not new. As we saw in the history of compost, Cleopatra valued worms so highly that she banned the killing and export of worms under pain of death. 

Early European settlers brought worms with them to America, although it’s not clear whether this was deliberate or accidental. Their value was certainly realised by naturalist Gilbert White. In 1789 he wrote:

“…worms seem to be great promoters of vegetation, which would proceed but lamely without them; by boring, perforating, and loosening the soil, and rendering it pervious to rains and the fibres of plants; by drawing straws and stalks of leaves and twigs into it; and, most of all, by throwing up such infinite numbers of lumps of earth called wormcasts, which, being their excrement, is a fine manure for grain and grass.” 

Charles Darwin was so fascinated he spent years studying and writing about them. In fact his book on worms initially sold faster than his book on the theory of evolution. 

Types of worms

As there are thousands of types of earthworms, covering every worm is slightly beyond the scope of this post. It is helpful to understand the different types, though. 

Anecic (out of earth) worms form vertical tunnels deep into the soil. These are large worms that feed on fresh litter at night which they drag into their burrows, but deposit their castings on the surface. They are reddish brown in colour.

Endogenic (within the earth) worms live further up in the soil. They range in size. Lacking in pigmentation, they can be blue-gray, yellow, pink or white. They form horizontal burrows in the soil.

If you are interested in vermiculture, you will need Epigeic (upon the earth) worms. They feed heavily on organic matter, are happy to be confined in smaller places and tolerate warmer temperatures than other worms. They are also small (usually less than 8cm in size), more lively than other worms and breed rapidly. 

The most common compost worm you will see sold is Red Worm or Eisena Fetida. These feisty worms have many names, including but not limited to red wriggler, brandling worm, panfish worm, trout worm and tiger worm.

Eisena Fetida allegedly produce a foul smell when handled roughly (hence the name Fetida, which stands for foul smell). According to the BBC, they also secrete a fluid which deters predatory flat worms. 

Eisena Fetida are resilient worms which reproduce quickly, and can tolerate a wider degree of temperatures, acidity and moisture. They are often considered the best option for use in worm farming. 

When you compost, watch out for little white worms (and possibly quite a lot of them). These are white pot worms or Enchytraeidae, and are an indication that your compost is getting acidic. 

How do worms eat

A worm’s mouth (called the porostorium) is a fleshy pad that looks like an extended lip – it is extremely strong but contains no teeth. 

Just behind the mouth is the pharynx. The worm eats by pushing the pharynx out of its mouth, using it to grab food and bring it back into its body.

Strong muscles break up the food, and small stones or grit in the gut also helps to break the food up. 

Worms lack the enzymes needed to digest food. Instead, their digestive channels contain bacteria which digest food for them. 

These bacteria do produce enzymes, which as we will see are incredibly valuable for the soil. They worms also contain tiny pieces of grit in their guts which help to crush the material they are eating. 

Worms eat a variety of foods, including: 

  • Fungi 
  • Nematodes
  • Bacteria 
  • Protozoa 
  • Organic material

Worm sex!

Worms are hermaphrodites i.e. they are both male and female. However, most worms need to mate in order to reproduce (although the red wriggler has been known to self fertilise).

When they are ready to mate, they develop a band (the clitellum). This is located around one third of the way down their body. 

When they mate, they line up inverted. Mucus is generated from the Clitella, coating the worms.  Sperm is exchanged, and directed down a groove into receiving pouches. The whole process takes an impressive 2-3 hours. 

A cocoon then forms on the worm. The worm eventually wriggles out of the cocoon, depositing both the eggs and sperms on the cocoon, which closes up on both ends. Each cocoon holds about 15 eggs. 

It takes 3 weeks or more for the cocoons to hatch. Different worm species take different lengths of time to reach sexual maturity, with the Red Wriggler taking about eight to ten weeks

How do worms communicate?

One fascinating study, chronicled on the BBC here, found that worms use touch to communicate and influence each others decisions. As a result, worms will sometimes move in the same direction, forming a herd or even a ‘worm ball’.

Why are worms good for compost?

Like all the other creatures in the compost pile, worms have a role to play – a particularly big one in this case!


Worms are considered shredders. They break up debris which then makes it easier for other organisms in the compost food web to digest them.  

Burrows and oxygen

As they burrow through the compost heap, they create pathways, aerating the compost and providing oxygen for the other organisms which turn organic material into compost. 

Vermicasts (worm castings)

Worm castings are rich in organic matter. In comparison to ordinary soil, worm castings contain: 

  • Seven times more phosphorus
  • Ten times more potash
  • Five times more nitrogen
  • Three times more * usable magnesium
  • One and a half times more calcium 

(Source: Teaming with microbes)

And it’s not just about the nutrients – it’s about the availability of those nutrients. 

Many nutrients in compost and soil are not available to plants because of chemical bonds. The enzymes in worm castings unlock these bonds and make them available to plants. 

Disease elimination

Traditionally, it was assumed that you needed hot composting to kill pathogens. However, research has since found that worms can also play a major role in killing diseases.

In one experiment, when a single worm was placed on a Petri Dish contaminated with e-coli, the e-coli was eliminated in just 20 minutes. (Source: Nicky Scott, How to Make and Use Compost.)

How to get worms in your compost

Worms have an incredible ability to find their way into compost. I have composted in closed bins on concrete in a closed greenhouse, and they have still managed to find their way in.

If you are worm composting, you will need to add worms. But what if you are using a more traditional composting method?

Worms will eventually find their way into your compost, so you don’t strictly need to add them. Still, it certainly won’t harm the compost, and it could help speed up the process. 

If you have a hot compost pile, wait until it has started to cool down before you add the worms. If worms are already present, they usually manage to migrate away from the heat before it kills them (although I have on occasion found dead worms in hot compost). However, if you drop worms into hot compost they could quickly die.  

When you do add worms to your compost, make holes in different parts of your compost, and add about 50 in each hole. 

An alternative to adding worms is to add earth, or even better a handful of compost from a maturing compost pile. These are likely to contain worm eggs which will soon hatch. Within 60 days or so these worms will start breeding, adding more worms again to your pile. 

Protecting your worms

A mole eating a worm.

From Moles

One problem with worms is moles, which can devastate the population of worms in a short time. This is not a problem with contained bins, but if you use a system with an open bottom moles can penetrate the heap. 

One solution is to use a screen at the bottom of the pile, which the mole can not penetrate through. 

From the cold

In most climates, even cold ones, the worms will find somewhere warm enough to survive the winter. However, you can encourage them to keep working on your compost pile by using an insulated compost bin or by insulating the compost pile with a material like straw. 

Why aren’t there any worms in your compost?

The compost heap is new.

While worms are amazing creatures, it can take them time to find the compost heap. If your heap is not likely to get very hot, you can add soil – this is likely to contain worm eggs. As mentioned above, you can also purchase worms and add them. If you just leave your compost, worms will eventually find them. 

The compost heap is too hot

Allow the heap to cool down. You can then wait for worms to find the heap or add them. 

Your compost heap is too dry

The compost process requires moisture and this can sometimes use up too much water. If it does so, the worms will leave and the compost process will slow right down. 

I like to turn my compost when this happens, wetting each layer with a hosepipe as I do so. Do be careful, as dry compost piles can produce harmful bacteria – it may be worth wearing a mask as you turn them. 

The compost has turned anaerobic

Most composters aim for aerobic (with air) composting. However, if the compost is too wet oxygen can not circulate and anaerobic (without air) composting can take place. Worms breathe through their skin, and if there is not enough air they will either leave the compost heap or die. 

High moisture levels can be caused by adding too many greens (high nitrogen material). To solve, add more brown (high carbon) material, with an emphasis on dry material such as shredded paper which can soak up the moisture. It’s also worth covering the compost heap if you are experiencing a lot of rain.

Learn more about greens and browns. 

They’re there, but you can’t see them

The behaviour of worms can vary from day-to-day. Some days I find a ton of worms at the top of my compost bin, and other days I don’t find any. It’s quite possible they are there, but you need to dig down to find them. 

Wrapping up

Whether you add worms or not, they usually play an incredibly important role in both your soil and your compost. Even better, unless you are worm composting, you don’t need to do much – they will usually just turn up of their own accord!