Can composting worms really double their population every 90 days? A lot of people make that claim. However, what I have heard is that they don’t double their numbers, but their biomass, every 90 days. And since most of the new biomass is juvenile worms, the total number of worms will be far more than double.
But can we really back up that claim? A lot of people starting out with new worm bins get frustrated at how slow the growth is, and how long it takes for a new bin to get established and the worm population to grow.
I decided to run the numbers. I did a computer simulation to determine the growth of a worm population over 100 days to see how fast the total biomass can grow under ideal conditions. I had the program draw a graph of the results.
I started with a few assumptions:
- An initial population of 1000 adult worms weighing 1 pound with no juveniles or cocoons.
- An adult worm will drop 3 cocoons every week.
- A cocoon will take 21 days to hatch.
- A cocoon will hatch an average of 3 worms.
- Newly hatched worms will take 42 days to grow to sexual maturity.
- It takes 400,000 newly hatched worms to make 1 pound of biomass
- It takes roughly 100,000 juvenile worms to make 1 pound of biomass.
The simulation showed results far beyond anything I have ever seen. In 90 days the initial population of 1000 worms grew to:
- Over 35,000 adult worms.
- Almost 79,000 juvenile worms.
- Over 114,000 total worms.
- An estimated total biomass of 54 pounds.
- 194,000 cocoons.
I don’t think anyone has ever seen real world growth coming anywhere close to these numbers. My experience shows that the doubling biomass every 90 days guideline is pretty accurate in normal worm bin conditions. But I have seen much faster growth in some conditions where we wouldn’t normally expect such growth. One fall, I tossed a handful of worms into some mulch in my yard. The following spring, there was a population of worms far beyond anything that could be explained by the worms doubling their biomass every 90 days. So growth faster than that is possible, even if you are never likely to see the kind of growth suggested by the simulation.
Even so, there are some things we can learn by looking at the graph.
- There won’t be any growth in the worm population for the first 21 days before cocoons begin to hatch.
- There won’t be noticeable growth in the biomass for the first 45 days before newly hatched worms put on some growth.
- The total number of adult worms will not grow until the second generation of worms hatch and mature at around 63 days.
- The total number of juveniles will start to grow rapidly after about 85 days when the third generation of worms begin to hatch.
When the simulation is run for 150 days, we learn a little more.
- The number of adult worms will start to increase dramatically after the third generation of worms reach adulthood at around 130 days.
- At this point, the total biomass and cocoon production will also start to increase dramatically.
So, what can we learn from this simulation about real world worm growth in a newly established worm bin? That you need to be patient. It can take 5 months or more before you see the kind of growth everyone has told you to expect. But after that, things can take off dramatically. Will your worm biomass double in 90 days? Maybe not in the first 90 days, but after that, it certainly can. And, given the right conditions, you may even see growth faster than that.