The Birds and the Bees of Composting Worms

January 10, 2026

Red Worm Life Cycle and Population Growth

Most people who end up interested in vermicomposting - especially the ones who actually get involved in this quirky field of endeavour - naturally end up curious about the life-cycle and population growth potential of the wiggly wonders that make the process possible.

In our “The Real Dirt on Composting Worms” article we looked at what makes epigeic earthworm species uniquely qualified for vermicomposting. Here, we will dig into the topic of their (rapid) population growth more deeply.

NOTE: For the sake of simplicity, and relevance for most home vermicomposters, we’ll be focusing mainly on Red Worm (Eisenia fetida/andrei) reproduction and their life-cycle, but we’ve included some comparisons with other composting species as well.

Factors That Can Affect Red Worm Population Growth

Something very important to hammer home right out of the gates is the fact that the growth rates of Red Worm populations can vary a great deal from one situation/system to the next. As such, you should never make assumptions about how fast your own population(s) will grow.

Here are some of the key factors of influence:

Temperature

As with other aspects of vermicomposting, this is definitely one of the major influences on Red Worm reproduction. Remember that an “ideal” temperature range for these worms tends to be in the 16 to 26 °C (roughly 61-79 F) range. Colder temperatures tend to slow everything down, so it should come as no surprise that a Red Worm population won’t grow as fast once temps dip down below the ideal range. What’s interesting, though, is that these cooler temps can actually stimulate cocoon production.

Moisture

Similar to temperature, moisture levels in a Red Worm habitat can have a huge impact on a population’s ability to expand in size. This is especially true with excessively dry conditions - but once again, similar to low temperatures, low-moisture conditions can also stimulate cocoon production (we’ll circle back to this further along).

Population Density

Many new vermicomposters can end up somewhat disappointed when their starter Red Worm population doesn’t seem to expand (or it even seems to decrease). While there are plenty of possible reasons for this (especially with newbies involved), a common issue is simply having densities of worms that are too high to stimulate further population growth. Stacking systems can be particularly bad for this, since each active tray tends to have a relatively small volume. On the flip side, low densities of worms combined with favourable conditions and resources can trigger rapid population growth.

Different Worm Species

While we are mainly focused on Red Worms here, many vermicomposters do at least “dabble” with other varieties - and there can be some fairly significant differences even among the main composting species. It’s also worth mentioning that when composting worms occur in mixed populations (quite common), it can result in competition between species, which can have a negative impact on population growth.

Food / Habitat Factors

As you might expect, quality habitat and nutrition can have a positive impact on population growth, while hazardous conditions and/or poor nutrition can slow it down - but, as is often the case in vermicomposting, there are definitely some nuances involved.

Circling back to the counter-intuitive cocoon production scenarios we touched on a minute ago…

Conditions usually considered to be “unfavourable" can actually stimulate the innate survival strategies in these earthworms. Remember, composting worms are “epigeic” - usually living very close to the soil surface or (often) above it, in rich deposits of organic matter. They tend to be much more exposed to rapidly changing, often harsh, conditions than their deeper-dwelling cousins.

Like most organisms, attempting to ensure the success of future generations is a key priority for these worms. There are a variety of adaptations that help them achieve this, but one of the most important is cocoon production. Cocoons aren’t just a way for earthworms to produce more offspring, they are also highly effective “seeds” for future worm populations that can often withstand much poorer conditions than the worms themselves.

NOTE: The worms in our indoor worm bins obviously tend to be a lot more pampered than populations in outdoor systems (and environments in general), but there are still survival triggers that can lead to cocoon production (e.g. dips in temperature/moisture, decline in habitat quality).

Myths and Misconceptions Relating to Red Worm Reproduction

Rates of Population Growth

A common Red Worm “fact” that has been floating around for many years is the idea that you can potentially expect your population to “double” in 60 or 90 days. This is a really interesting one given that it’s completely and utterly wrong…and yet has the potential to also be correct. 😂

We will be circling back to life-cycle timelines in more detail further along, but the long and the short of it - and something that might surprise a lot of readers - is that the “doubling” idea (within those time-frames) is actually a vast underestimate! Even in worm bins that aren’t particularly optimized, it’s not uncommon to see much higher growth rates (a “real world” example will be shared later).

But alas, it’s a bit more complicated than that…

For starters, we’ve already hit on some factors that can really toss a wrench in our well laid worm population growth plans. Yes, even certain “bad” conditions can stimulate cocoon production, but there’s no rule that says cocoons must hatch within a certain time-frame (and like we said, they can be an excellent survival strategy for conditions the worms themselves may not be able to survive). Bottom-line, factors like cold temps, dry conditions and overcrowding can very easily bring population growth to a near stand-still. So, there are indeed plenty of cases where aiming for doubling in a handful of months might not be such a bad goal.

There is also the question of what exactly is “doubling”? The assumption is almost always that it’s the number of individuals in the population. That’s how we think of it for humans and plenty of other animals, right? Well, Glenn Munroe, in his excellent “Manual of On-Farm Vermicomposting and Vermiculture” (2004) mentions the potential doubling of Red Worm biomass in 60 days when conditions are favourable.

That’s a completely different ball game! You can think of biomass as basically the total volume/weight of worm bodies, so it has more to do with the average size of your worms than the number of individuals (although that is certainly important). In other words, even if you have 20X more worms after 2 or 3 months, a lot of them will likely still be smaller, immature worms, which obviously won’t have the same biomass as adults.

NOTE: It is beyond the scope of this article to get into the ins and outs of adults vs juveniles in terms of waste-processing potential (etc), but it’s important to be clear that adults of a given size aren’t automatically as valuable as (let alone more valuable than) the number of juveniles needed to make up the same biomass. If anything, having far more young worms is likely going to be a better scenario than fewer larger/older worms, especially over the long-haul.

It’s worth mentioning that you can also find some clues for the potential origin of the “doubling in 60-90 days” idea in old worm farming manuals (e.g. various guides released by Shields Publications*). A commonly recommended expansion method involves “splitting” beds after 60 to 90 days, suggesting that the biomass of worms has doubled by that point (since professional worm farmers tend to be more interested in big worms than having lots of smaller worms).

*For decades, Shields Publications was a very popular publisher of books relating to earthworms, vermicomposting and worm farming, but they seem to have shut down their operations.

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Worms Lay “Eggs”

This one is pretty minor, but a lot of people assume that the term “cocoons” simply refers to worm eggs. In reality, the cocoon is actually a vessel designed to hold (and protect) multiple fertilized/developing eggs. We will come back to this in the life-cycle section.

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Different Species Can Interbreed

Another misconception some people have - often due to information shared by less reputable worm sellers (looking for any way to uniquely position their product) - is that different earthworm species can interbreed successfully, resulting in special “hybrid” worm varieties.

This is completely false. While technically possible, the hybrid species would need to be created in a bio-tech lab, not simply by putting different worm breeds together in the same system.

As an illustration of this, two very closely related species, Eisenia fetida and Eisenia andrei, are known to commonly live in mixed populations, but it has been determined scientifically that even they cannot interbreed successfully (Sheppard, 1988).

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A Red Worm Population Will Eventually Overrun a Worm Bin

Some people assume that their worms will just continue breeding and growing in number until their system is completely overrun (basically overflowing with worms).

While we can’t promise you that some of your worms won’t try to escape at some point (be sure to check out “Why are my worms trying to escape?”), we can say with certainty that a Red Worm population is pretty good at self-regulation!

You may even recall that one of the limitations discussed earlier - namely population density - addressed this directly. High population densities typically serve as an indicator that all is well, and population growth will slow accordingly. More cocoons may still be laid - especially if there are other potential warning signs of a rough road ahead - but most of them will likely remain unhatched until the conditions are more favourable.

Bottom-line - while you may see some pretty incredible densities of worms in your systems at times (e.g. when you are doing a fantastic job of optimizing their environment/nutrition), the population can’t just expand forever. 😎

As a related sidenote, isopods (woodlice, “rollie pollies”) - another valuable composting system critter - do seem to showcase more of an “endless” breeding strategy, as anyone with a thriving isopod bin can likely tell you! The big difference? These creatures are highly mobile in comparison to worms. In their natural environment (and most outdoor systems) pregnant females can easily roam off in search of greener pastures, so it is a lot less likely that a population will end up so crowded that it creates a hazardous environment.

The Red Worm Life-Cycle

There are 3 main stages of an earthworm life-cycle:

cocoon,
juvenile, and
adult.

These could be further broken down (e.g. hatchling, young adult etc) but there isn’t any real advantage in doing so here. As you might expect, the timeline (and overall success) of this life-cycle is greatly influenced by a wide range of factors including the major ones we looked at earlier.

Earthworms are hermaphroditic, meaning they have both male and female reproductive organs, but most varieties still engage in a form of sexual reproduction involving the exchange of sperm. The sexual organs are located in an earthworm’s clitellum, the somewhat swollen band of tissue located just behind the head region of Red Worms and other members of family Lumbricidae (this structure can actually be quite flat in some other earthworm families).

NOTE: Parthenogenesis - asexual reproduction - is known to occur in some species (not Red Worms), but it isn’t necessarily the sole means of reproduction in those varieties (Edwards and Bohlen, 1996).

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Characteristics of Adult Red Worms

If you are wondering how you can tell mature worms from immature worms, we have some good news…and some bad news. 😄

The good news is that if you see a prominent clitellum, you can be pretty sure you’re looking at an adult! Size can also be somewhat helpful as well. If the worm is at least 2 or 3 inches (5-7.6 cm), there’s a decent chance it is fully grown.

The bad news, however, is that just because you don’t see a clitellum, it doesn’t necessarily mean you’re looking at an immature worm. Various factors can result in clitella being a lot less obvious. To compound this, there are plenty of situations where fully mature worms are very small. E.g. in systems that are: too dry, overcrowded, lacking in nutrition.

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Mating in Red Worms

Adult Red Worms come together head to head, connecting on their ventral (lower) sides with their clitella lined up. If you happen to catch a couple of your worms engaged in the act, the “good news” (depending on your perspective) is that mating pairs aren’t as responsive to stimuli such as touch or light - so it can often be quite easy to observe the mating process.

Large quantities of mucus are secreted in the region where the clitella overlap, creating “mucus tubes”, which help with the transfer of sperm between worms. Once mating is complete and the worms separate, the clitellum of each worm releases a secretion that hardens into a ring around this region, into which sperm and eggs are released along with a form of albumin fluid. The ring is then gradually worked off of the worm body, and sealed to form the cocoon. (Edwards and Bohlen, 1996)

NOTE: This helps to explain why you can see concentrations of cocoons in certain rough materials like shredded cardboard, burlap, and hemp blankets - since these materials can greatly assist the worms in drawing the ring off of the body.

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Red Worm Cocoons - In More Detail

Cocoons are quite easy to spot in a worm bin…once you develop an “eye” for them (which, admittedly, can take a bit of practice). They tend to be ~ 3 or 4 mm in length, and are shaped like a little lemon or teardrop - most often with a straw-like colour (but coloration can vary from creamy yellow all the way to dark brown, depending on age).

New vermicomposters sometimes mistake white mites for cocoons, since they do indeed little like little eggs - but the bright white colour and smaller size (and sheer number of them in some cases) should always be a giveaway.

FUN FACT: The Giant Gippsland Earthworm, Megascoledis australis - which has an average length of 1 metre, but with recorded lengths of nearly 3 metres - is thought to produce the largest earthworm cocoons, measuring up to 75 mm x 20 mm - about 3 inches x 0.8 inches (Edwards and Bohlen, 1996). You wouldn’t have any trouble spotting those! 😉

It’s important to note that mating is not required for every single cocoon produced. Since sperm is exchanged between worms during copulation and then stored, the worms can continue using it to fertilize eggs in new cocoons until the supply runs out.

How many cocoons can an adult Red Worm produce in a year?

Apparently a lot!

Data from well-known Australian worm farmer, George Mingin, reports an average of about 3 cocoons per (adult) worm per week (Christie, 2013).

Edwards (1988) reported even more than that: 198 cocoons per year for Eisenia fetida (3.8 per worm per week), 188 for African Nightcrawlers, Eudrilus eugenia (3.6 per worm per week), 1014 for Blue Worms, Perionyx excavatus (a whopping 19.5 per worm per week).

Blue Worms are thought to have the ability to alternate between sexual and parthenogenetic (asexual) reproduction. Interestingly, they actually have a somewhat slow growth rate, but they mature more quickly and produce a lot more cocoons than other composting species (Reinecke and Hallat, 1989), likely helping to explain why they are able to take over Red Worm populations when conditions are favorable!

Each earthworm cocoon can contain many fertilized eggs, but often only a fraction of these result in viable hatchlings.

In terms of incubation time (how long it takes for the hatchlings to emerge), George Mingin reports an average of 14-21 days. This is definitely on the “fast” end of the spectrum. It’s very important to remember that this data comes from a professional who needs to have his breeding/growth process completely dialed in, so it’s not necessarily representative of a typical worm bin. We share it simply to show what’s possible! (That said, stay tuned for some pretty impressive “normal worm bin” results a bit further along)

Edwards (1988) reported incubation times of 32-73 days for E. fetida, 13-27 days for E eugeniae, 16-21 days for P. excavatus.

As always, there are quite a few factors that can significantly influence incubation - but it’s certainly not unreasonable to predict that, in a typical worm bin, many cocoons will hatch within 30-60 days (1-2 months), assuming climate-controlled conditions and the worm population having some room to expand in size.

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Red Worm Juveniles

Similar to cocoons, hatchlings can be quite elusive in a worm bin due to how small (easily hidden) the baby worms can be when they first emerge.

They tend to be pinkish in colour, and more translucent (“see through”) than older worms, but common Red Worm features (e.g. yellowish tail tip) can sometimes be visible.

An organism commonly mistaken for baby Red Worms is the White Worm (aka Pot Worm) but, similar to the mites mentioned earlier, these are very bright white. They are also quite thin and usually longer, while little Red Worms tend to be a bit more “chubby” and “stubby”.

As juveniles get older, they look more and more like full-grown adults in terms of coloration and size. As touched on earlier, the main distinguishing feature is the lack of clitellum, but again, this isn’t always a foolproof way to determine if a worm is mature.

The time required for Red Worms to reach sexual maturity can be as little as 6 weeks (Christie, 2013), maybe even less - but at the risk of sounding like a broken record here, once again, this is going to be highly dependent on the factors discussed earlier (among others), and certainly not what you should expect to see in typical home worm bin.

Still, let’s summarize George Mingin’s data, just so you can see it all in one place, and know what’s possible:

3 cocoons per adult worm per week
3 hatchlings per cocoon
3 week cocoon incubation (technically he says 14-21 days, but rounding up makes sense)
6 weeks from hatchling to adult

So, as little as 9 weeks from start to finish.

Looking at these numbers, it becomes quite easy to see how a “doubling” (of a population size) within 60 to 90 days should be fairly easy to surpass!

Need Some “Real World” Inspiration?

PC’s very own “Worm Guru”, Bentley Christie, has been fascinated with Red Worm population growth for many years - and involved in his fair share of experiments along the way (some of them he admits to being a little “hare-brained”).

Something that has become quite clear (and important) on this journey of discovery is that George Mingin’s “ideal” data isn’t necessarily all that unrealistic, even with fairly normal systems!

As a key example, in the fall of 2022 Bentley set up a pretty basic 5 gallon worm bin, adding only 25 adult Red Worms as his starter population. After 11 weeks of operation (i.e. just shy of the 3 month mark) he painstakingly counted all* the worms and cocoons in the system.

The results were pretty staggering!

He found:

193 Adults
1656 Juveniles
476 Cocoons

In other words, the number of adults, alone, had increased 8-fold in less than 3 months, while the total population had increased nearly 74-fold!

*As a sidenote - the leftover material from a previous (and very similar) trial was left to sit for 12 weeks, just to see if a new population would develop (proving that not all juveniles and/or cocoons had been found - even with very thorough counting methods). Sure enough, 321 worms and 288 cocoons were recovered from this material (and it’s important to note that the counting approach was far more lax in this case than for the actual trials)! 😎

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Red Worm Life-Span

Some people will naturally wonder how long they can expect their precious Red Worms to live.

Well, the good news is that In protected cultures - well-maintained, indoor worm bins could likely be included in this category - Red Worms have been found to live for well over 4 years. As a comparison, that’s potentially more than the average hamster or gerbil lifespan!

That being said, it has been suggested that the lifespan in more “wild” environments (likely including outdoor composting systems) is usually much shorter than this (Edwards and Bohlen, 1996).

KEY TAKE-AWAYS

Epigeic earthworms, such as Red Worms (Eisenia fetida/andrei) have characteristics and strategies - such as much faster reproduction - that make them better suited for vermicomposting than soil-dwelling species.
There are, however, quite a few factors that can greatly influence the life-cycle timeline (and population growth as a whole) of composting worms, so all stats relating to this shouldn’t ever be considered set-in-stone.
Major factors of influence include temperature, moisture content, population density and food/habitat quality (but there are definitely others that can play a role).
Low temperatures, low moisture content, low habitat/environmental quality and low nutrition can all slow down population growth, but…
These less-than-ideal scenarios can often stimulate cocoon production, since cocoons are much better adapted for survival than the worms themselves.
There are a number of common myths and misconceptions relating to Red Worm population growth, but likely the most widely spread/accepted of these is the idea that a population of Red Worms can “double” in 60-90 days.
This can be a reasonable estimate when thinking in terms of biomass (not population size), or if conditions are quite unfavourable, but in most cases this is going to be a vast under-estimate of actual population growth.
The Red Worm life-cycle is made up of 3 main stages: 1) cocoons, 2) juvenile worms, and 3) adults.
Data from well-known Australian worm farmer, George Mingin, tells us that under ideal conditions, adult Red Worms can lay 3 cocoons per week; cocoons can hatch within 21 days; each cocoon releases an average of 3 hatchlings; and juvenile worms can reach adulthood in 6 weeks.
It’s important not to assume you will see similar results in a regular worm bin - but real world results from PC’s “Worm Guru” seem to suggest that these sorts of stats may be more attainable than you think!
When properly taken care of, Red Worms have been found to live for more than 4 years, but their life-span can be reduced significantly in more “wild” environments.

We’re a bit biased, but we feel the topic of Red Worm population growth is pretty darn fascinating - and we’re hoping to continue delving more deeply into it with our own worm growth trials and other related experiments.

If this is something that floats your boat as well - especially if you’d like to start your own population growth experiments - we’d love to hear from you!

REFERENCES CITED

Christie, B. (2013): Will a Red Worm Population Double in 3 Months?
RedWormComposting.com.

Edwards, C.A. (1988) Breakdown of animal, vegetable, and industrial organic wastes by earthworms. Agric. Ecosyst. Environ., 24, 21-31.

Edwards, C.A. and P.J. Bohlen (1996) The biology and ecology of earthworms (3rd Edition). Chapman & Hall, London, 426pp.

Munroe, G. (2004). Manual of On-Farm Vermicomposting and Vermiculture. Organic Agriculture Centre of Canada.

Reinecke, A. J., and Hallatt, L. (1989). Growth and cocoon production of Perionyx excavatus (Oligochaeta). Biol Fertil Soils., 8(4), 303-306.

Sheppard, P.S. (1988). Species differences in cocoon and hatchling production in E. fetida and E. andrei, in Earthworms in Environmental and Waste Management, (eds C.A. Edwards and E.F. Neuhauser), SPB Acad. Publ., The Netherlands, pp. 83-84.

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