(possibly) The first and only red wiggler reproduction calculator on the web – by me!

Some time ago, I started vermicomposting in a couple bins with a small number of red wigglers I bought locally. I spent a while trying to guesstimate how long it might take for reproduction.

“Word on the web” was a little all-over-the-place (but tended to point to doubling in the 60-90 day mark), so I looked into a couple research papers.

Turns out… red wigglers are prolific breeders! Some pencil-math using the research data showed massive reproductive growth. Unfortunately, trying to chart something like that by hand was time consuming and a little tricky.

I initially thought I’d throw together a quick text-based program in Java or C to get some real data spit out, but eventually decided that I may as well make something a little nicer-looking for the web.

A couple days later, and…

Vermicompost Calculator

Voila! Clicking that image will take you to the calculator page by the way.

It’s got most of the basic options you’d want when calculating worm reproduction, and despite the numerous options, I *think* I’ve made it pretty simple to use. It’s also been tuned so that it should handle more than a million worms without slowing down too much or causing the web browser to hang. Time will tell.

If you’d like to check it out, it’s right here on the site:


With that out of the way, that page originally had a bunch of stuff in the questions/answers section which kinda delved off into more generic vericomposting answers and made it fairly long. Thus, I’ve moved them here:

Q: It says my 10 worms will become 26.6 trillion in 2 years. Will I need a bigger bin?

A: Usually by the time the chart starts reaching exponential increases, you’re starting to get out of a realistic ballpark for growth rate. At some point, your worm’s environment won’t support high growth, and your rate of growth will really taper off.

But just for fun, let’s see what we’d need to support those 26.6 trillion worms:

  1. 26.6 trillion adult worms alone (no babies!) would weigh about 26.6 million pounds (at 1000 adults/pound).
  2. To keep the worms producing quickly, we’d probably want a “stocking density” of about 0.5-1 pounds per square foot. We’ll go with 1 to make things easier. That means we’d need 26.6 million square feet of space. The good news is, that’s just under 1 square mile which is technically possible to pull off. The bad news is that we’re no longer in rubbermaid-bin territory.
  3. If we want to keep the reproduction going at the chart-rate, we need a climate-controlled building where we can keep temperature/humidity at optimal levels. With a large warehouse or multi-story building we can keep from needing it to be 1 square mile in size, but it’ll still need to be large and thus won’t be in reach for most hobbyists. For the sake of argument we’ll assume we’re filthy rich, have a booming worm business that can support it, and/or find a deal.
  4. The common notion is that worms will eat their own weight in food every 1-2 days. So 26.6 million pounds of worms will probably need 13-26 million pounds of food per day. Kitchen leftovers won’t cut it here, and only 1.2 million pounds of food (roughly) is wasted each day in developed countries. This is where things start to fall apart, 26.6 million pounds of anything is a lot.

Looking back from a hobbyist point of view, even if we have a lot of space, food is clearly going to become a factor very early on.

Q: Does the calculator have any hidden glitches/gotchas?

A: Yes. Aside from assuming you can provide a perfect environment even when you start approaching thousands/millions/billions of worms (as seen above), there are a few technical ones. Some things might take +/- 1 day to occur, and it’ll let 1 solo adult worm reproduce without a mate. Bigger issues like the graph not working at all are likely to be web-browser specific – let me know if you run into this along with your browser details.

Worm weight (if enabled) is an area where the calculator uses a fairly simple/dumb algorithm. The weight-gain math is based on the V&R study. However, the calculator currently assumes any Original Adult worms are “freshly matured” (were immature wormlings the day before). There are a lot of other variables that’ll affect actual worm-weight too. In any case, take the weight values with a grain of salt, and don’t use them as much more than a possible ballpark. There are way too many variables to get anything close to perfect accuracy when it comes to ” X worms ~= Y weight “.

Q: My red wrigglers aren’t making many babies. How do I get the same results as the simulator?

A: There are a few key aspects that most of the experiments (used for the calculations) share.


Around 80% humidity is common. This is really hard to pull off in a small-scale bin.

If you’re using a plastic bin and only have holes in the top, chances are that if you’ve got 80% humidity near the food, you’ve got 100% humidity in the bottom, causing anaerobic conditions (anaerobic = “without air” = worms will die if they sit in that area). On the other hand, 80% humidity in the bottom means the top is probably too dry. You can try using a lot of loose bedding in the bottom to help with airflow (and add dry bedding to the top when it’s too wet), but enclosed bins are usually a matter of just trying to keep the worms alive.

If you’re using a plastic bin with holes all over (including the bottom), or any other type of bin that allows good airflow and drainage out the bottom, drowning the worms becomes a lot harder. In this case, the material tends to dry out a lot quicker. If the food isn’t wet enough to keep the bin at high humidity, using a spray bottle to mist a lot of water periodically can really help. Avoid directly pouring water in the bin because it tends to compact the bedding.

Regardless as to what type of “worm home” you’re using, keep in mind that the bigger the space, the easier it is to keep moisture levels consistant. A 100L bin that’s half full and brought to the correct moisture level will maintain it’s moisture level a lot more easily than a 10L tub. And if conditions get too wet or too dry, the 100L bin will offer a larger region that the worms can retreat too if problems arise.


For red wigglers, it’s pretty unanimous that 25 degrees C is the ideal temperature for growth and reproduction. Chances are that indoors is the only way you’ll pull this off. Find a good temperature-controlled area in your home out of the sun and give that location to your bin. Keep in mind that food decomposing in your bin will generate some of it’s own heat, so don’t go setting your thermostat to exactly 25!

If outdoors or in another less-than-ideal situation, be creative and do your best. If the area tends to get too warm, at least find a place away from sunlight and make sure humidity doesn’t get too low in the bin if your area has a dry heat. If in a cool region, an area that doesn’t get *as* cold like a garage might be worth investigating. Keep in mind that your red wigglers will start dying if the temperature gets near freezing or gets near 35C on the warm end.

Keep in mind that most of the research is done at carefully controlled temperatures. If you can’t match it, your own results won’t be as strong.


Crowding usually isn’t an issue in the lab because they generally remove “newcomers” from the original container, weigh/observe it, and transfer it elsewhere to monitor during the duration of the study.

Chances are you won’t be doing that, so a few pointers below to help keep your own situation from becoming overcrowded.

If the worms are feeling crowded in the bin they’ll lose interest in reproducing, as often happens in nature. Creatures will often procreate very quickly up until a certain population point. On the other hand, if they have way too much space, there’s notion out there that the worms might not find each other to mate – I haven’t read any studies that confirm that, so if you’re aware of one please let me know.

Generally, 1-2 pounds of worms per square foot of space is considered to be a common “stocking density”. If you want faster reproduction, moving down to 0.5 pounds of worms per square foot of space might be worth investigating, and I’ve read at least 1 document that listed that as a reasonable minimum. If you’re looking to instead just see how many worms you can pack into a space and aren’t concerned about a drop in reproduction, I’ve heard of 4 pounds per square foot of space, although you should expect very low reproduction at that density and if conditions were to suddenly become poor, expect a number of those worms to quickly die.

Short version here is that more space is better as long as your worms are in close enough proximity to each other that you’re seeing cocoons. Few worms in a large space does mean you have to be a little more careful about overfeeding.

Side note: If you get hung up on the “X pounds per square foot” bit, it’s commonly claimed that there are approximately 1000 Adults in 1 pound of worms (you can play with the calculator to get other combinations such as 400 Adults + 1700 Young, but be careful here because the calculator has a tendancy to low-ball the weight of any original adults in the bin).

  • A bin that is 1.3×1.6 feet is about 2 square feet, so in such a bin, 1000 adult worms would be 1 pound in 2 square feet, or 1/2, or 0.5 pounds per square foot.
  • In the same bin, 2000 adult worms would be 2 pounds in 2 square feet, or 2/2, or 1 pound per square foot.

Food Quality and Quantity

In most lab studies, worms generally received the same type of food over and over again, in predictable, carefully measured amounts. Chances are the food your worms receive won’t be as consistent or boring.

I’ll start this by backtracking on Quantity. Many people kill their worms with too much food. The problem isn’t the worms overeating – they eat what they can eat. The problem is that too much decomposing food can start fast-composting on it’s own, and/or quickly cause anaerobic conditions. Both create heat that will force worms to flee from the food into their bedding. Instead of eating they’ll be trying to find a place in the bin where they won’t die! Even worse, this rapid decomposition can add high water content to the bin while it sucks oxygen out of the air – so whatever place the worm finds that *was* safe might become a death trap.

So don’t overfeed your worms. They can live for weeks just on the copious amounts of cardboard/paper bedding (that you *should* have) and leftover food bits distributed throughout if need be.

That said, for high reproduction, you do want food to be consistently available. It doesn’t have to be a lot – there just has to be something in there, slowly decomposing, that they can feast upon. If you get a bad smell coming from the bin, it’s a sign that you’ve got too much in there – if it really *is* a small amount, cover it with some fresh bedding – otherwise, take it out.

When it comes to quality, we’re not talking 5-star cuisines…. after all, one of my preferred studies (V&R) used cattle manure. For high reproduction, you want food that worms will like.

The majority of moist kitchen scraps will normally be fine. Melons in particular (canteloupe, muskmelon, watermelon, etc) are big favorites for worms – I’ve found they’ll ignore everything else and head for the melons. Make sure to balance food with bedding.

Avoid things that have a strong non-sweet flavor (citrus, onions, anything that had salt, etc). Animal products like meat and dairy will tend to cause more trouble than they’re worth – if the rot and smell doesn’t bother you, a rodent getting into the bin will. Root crops (potatoes, carrots, etc) are fine but keep in mind they’ll take a very long time to break down to the point where worms will eat them – there’s a reason the worms left them alone in your garden all summer long.

When feeding, feed a small area of the bin at a time. The worms will find it, and if something goes wrong, they can retreat in any direction. Cutting up food into small pieces (or blending it) are options that a number of people choose – more surface area allows the food to break down more quickly and gives the worms food sooner.

Diversifying food when possible is a good idea – if a certain food is causing problems for the environment of your bin, diversification will keep you from adding too much of it and give time for everything to balance out.

Above all, bedding, bedding, bedding. Ample food is good, but the bin should always have an abundant supply of carbon-based bedding (such as shredded cardboard/newspaper). This not only helps provide aeration while balancing out the nitrogen-rich foods, but also gives the worms a nice safe edible home to spend time in when they’re not actively eating the fresh scraps you dumped in.


Depending on your situation, you may not be able to perfectly match the lab conditions of ~80% humidity, 25 degrees C, and an ideal non-crowded environment while maintaining ample food source. After all, your job probably doesn’t involve growing worms in a research lab. But the closer you’re able to come to hitting those targets, the higher the chance that you’ll come near to the results.

If you have the room, 2 separate bins might be worth maintaining. Not only do 2 bins allow you to conduct your own A-B testing, but if you do something horribly wrong in 1 bin, you always have the 2nd one to fall back on.

Q: I seem to get a long “flat line” in the calculator/chart. Bug?

A: Usually it’s not a bug. Early on in the chart, and depending on what your “start” worm setup was like, it’s not uncommon to get ranges of time where… say… some cocoons are hatching at the exact same rate that hatchlings are becoming adults. Or cacoons are becoming hatchlings at the same rate they’re being laid. This happens more frequently if you’ve used small values (like starting with a couple worms).

This admittedly looks really odd when it happens – during development I admittedly spent time chasing down a few “bugs” that turned out to simply be this behavior. That said, there could be real bugs that I’ve missed – look very closely at everything going on, extend the date range by an additional few weeks, and slowly math it out on your end. If you’re convinced it’s a bug, leave the details of your setup (numbers used) in the comments below and I’ll take a look.

Q: Every time I change my browser window size to fit the chart, the chart changes size on me! Is this site possessed!?

A: I sure hope not! As to the chart changing size, the bigger your browser window is (height), the taller it makes the chart. Try making your browser window really tall (or really short) and see if it helps get the size you’re looking for. If the chart ends up horribly broken no matter what, please let me know what screen resolution you’re using.

Q: I think my red wigglers are dying. They’re all curled up in a ball in the corner of the box and not moving much. What should I do?

A: If they’re all grouped together in that corner, there’s undoubtedly something in their environment that’s severely stressing them out. Piling into a ball is basically a worm’s last-resort “survival mode”, but doesn’t always indicate anything specific… you kinda have to “check everything”. A few things to check off the list:

  • Temperature – is it really cold or really hot? (say… below 15C or above 30C)
  • Humidity – check a few locations in the box and pull out some vermicompost. Is everything dripping wet? Alternately is the material really dry (say 50% humidity or less)? If you think it might be 1 of the 2, the worms probably went to the “best” area of the box they could find before curling up which might help narrow this down.
  • Airflow – particularly if the box was pretty wet, is everything compacted (less air) or is the bedding still fluffy (more air)? Did the worms move to an area nearer to some air holes (or the top) before curling up?
  • Disturbances – worms don’t like vibration, light, noise, being jostled around, being moved, etc. Basically anything opposite of still, quiet, and dark. Was there anything nearby that caused a lot of vibration (or a noise loud enough to cause vibration) recently? The good news (if it’s this) is that they’ll recover once it’s still and quiet for awhile.
  • Toxic environment – is there a lot of food in the top of the bin, or did you recently add a lot of something (peat moss, etc)? Is there an undesirable food in the bin (citrus, onions, something that contains salt)? If you saw this and immediately said “oh I know what it is…”, you may want to make a fresh bin for the worms. If you’re not sure, you can try moving everything to 1 side of the existing bin and put lots of deep fresh bedding in (wet shredded newspaper/cardbord) and place the worms on top in the new area. Generously mist the worms with some distilled water and put the lid on. Check back in an hour or two and see if they’ve moved down (if not, mist them again and cover them with a few pieces of wet shredded newspaper to keep them moist while you continue troubleshooting).

If you end up in a situation where you’ve corrected a problem but aren’t sure if you’ve solved the issue, remove any food and drop piece of melon somewhere in the bin – check back a little later – if you lift the melon and find a bunch of worms inside, they’re probably on their way to being happy and healthy once again. If a few days go by and there’s no sign of the melon being touched, something’s usually quite wrong and you’ll probably want to re-do the entire bin before the worms all die.

Q: My worms are trying to escape my bin! Why don’t they like it?!

If these are “new” worms (just added to the bin), it’s not uncommon for a few of them to roam. If this is the case, just give them a couple days to settle down.

If you’re witnessing a mass-exodus though, there’s something wrong in your bin – quite possibly a toxic environment that’s so bad they’d rather take their chances on the outside. Read through the items in the answer above and see if anything catches your eye.

If it’s not a new bin, not a mass-exodus (all worms healthy), has a lot of worms, and just a few periodic runners, there’s a chance your bin is overpopulated. When the population of a bin gets really high, the adult worms are the first to try leaving. If you have another empty bin nearby, you can try splitting the bin, go fishing, or give away some worms!

Leave a Reply

Be the First to Comment!