by Brian Tomasik
First published: 25 Dec. 2017; last update: 16 Jan. 2018

Summary

Vermicomposting (composting using earthworms) is a popular eco-friendly method for disposing of home food scraps. Unfortunately, worm composting forces large numbers of invertebrate animals to be born without their consent into short lives that soon end with painful deaths. In addition, worm composting involves some inevitable direct harm to some of the worms and other critters inhabiting the compost bin. For these reasons, I oppose vermicomposting and suggest disposing of food waste in other ways that give rise to fewer invertebrates.

Introduction

For many years, a friend of mine has maintained a vermicomposting bin for disposal of food waste. Since I'm troubled by invertebrate suffering, I insist on managing this worm bin in an effort to minimize the harm done to the bugs in the bin, even though I strongly oppose my friend's having the worm bin in the first place. Through these years of managing worm bins I've become acquainted with different harms that befall the residents of a worm bin.

Here are some videos of invertebrates in my friend's vermicomposting bin:

Eisenia foetida R.H. (2)The most significant harm caused by worm composting in my opinion is that such composting brings into existence enormous numbers of invertebrates—both worms and smaller animals—who may suffer during their short lives and will probably suffer in the process of dying. No being consents to its birth, and some of these animals face short, miserable lives, especially when competition or poor environmental conditions lead to low survival rates for newly hatched offspring. I believe this suffering is not compensated by the pleasure that some of these invertebrates also feel during their lives, in a similar way as the suffering of the young child in the fictional city of Omelas is not compensated by the pleasure of the city's other inhabitants.

In addition, the process of managing a compost bin gives rise to direct harm to some number of invertebrates, as I'll describe later in this piece.

Numbers of invertebrates

Tomasik ("Abundances ...") compiles estimates of invertebrate densities in soils. For example, the Brady (1974) table shown in that piece reports 30 to 300 earthworms per square meter of soil, as well as 103 to 105 of other non-nematode invertebrate animals. A compost bin probably has more juicy food to be eaten than does a typical patch of soil, so the density of earthworms and other bugs per square meter of a compost worm bin is probably higher than the Brady (1974) numbers. On the other hand, a small home composting bin will often be less than one square meter in size.

While I haven't done a rigorous estimate, by eyeballing my friend's worm bin, I would guess it contains on the order of 102 earthworms. I've also estimated that my friend's bin contains perhaps hundreds of thousands of springtails, mites, and other tiny non-nematode animals. So the Brady (1974) numbers for invertebrates per square meter seem about right, or maybe on the low side, as numbers of invertebrates in a single person's vermicomposting bin.

Direct harms caused to worm-bin invertebrates

In addition to suffering from natural causes, worm-bin invertebrates can be harmed in various other ways. It's possible that some of the problems I describe could be avoided by a more experienced vermicomposter than I am, but some of these causes of harm seem inevitable.

Changing conditions

Changing conditions in the worm bin cause changing populations of organisms. For example, if the bin becomes dry or anaerobic in some regions, then invertebrates in those regions may die or at least languish. As the temperature declines in winter, flying insects are likely to die off or become less active, in my experience. The flux caused by new food will inevitably create winners and losers among the biotic community in the worm bin.

If the bin is poorly maintained, such as because the owner forgets to add water or lets it get too cold in winter, then invertebrates may die off en masse.

Crushing

If there are flies or other fragile insects near the surface of the worm bin, then dumping new food into the bin may crush or at least trap these insects. Meanwhile, digging in the bin to bury new food scraps will also crush some bugs, such as beetles or springtails. Wikipedia ("Vermicompost") recommends "occasional stirring of bin contents" for aeration, but doing so is liable to maim some invertebrates, as a result of which I personally avoid stirring.

I've found that tiny animals like mites tend to crawl over a plastic worm bin, and putting a lid over the bin is likely to crush some of these tiny creatures. I try to reduce this problem by laying the lid gently on the top of the bin at a slight angle rather than popping it onto the plastic container the way you would if you were sealing the container's contents. Leaving the lid askew also allows air to enter. (If you for some reason don't leave the lid askew, make sure there's some other way for air to enter the bin, such as not-too-small holes in the lid. I don't know how much air access is needed to support the organisms in the bin, but I err on the side of being too generous with air access.)

Escaping

Wikipedia ("Vermicompost") explains: "Worms generally stay in the bin, but may try to leave the bin when first introduced, or often after a rainstorm when outside humidity is high." My friend's worm bin is indoors, so I don't have the rainstorm problem, but I have occasionally had problems with worms escaping, especially when starting a new bin. Even once the bin is stable and most worms stay inside, I occasionally see one or two shriveled-up worms on the outside of the worm bin, indicating that worms ventured outside the bin and then dried up.

If the worm bin breeds beetles or other mobile insects, these critters are even more likely to wander outside the bin. This can leave a basement floor littered with scattered beetles or winged insects that escaped and couldn't get back in. They either dry out or are stepped on by my friend. I try to blow them out of the way when I venture into the basement.

When the beetle population was particularly high, I sometimes had the experience that after I added water to the worm bin, the beetles would come to the soil surface to avoid drowning, and tens of beetles would spill out onto the floor. I tried to gently put some of them back into the bin by scooping them onto a sheet of paper, but often the task was too daunting, and the basement floor remained littered with beetles. (Since that time, the beetle population has subsided, due to the seemingly random fluctuations in faunal composition in the worm bin.)

Drowning

Wikipedia ("Vermicompost") explains: "Bins need holes or mesh for aeration. Some people add a spout or holes in the bottom for excess liquid to drain into a tray for collection." My friend's worm bins used to have holes in the bottom to let water drain out and let air in. However, I found that small larvae tended to fall through these holes, and they would either drown (if they fell into a pool of leachate) or desiccate (if they fell onto a dry surface).

To avoid this problem, I began using plastic worm bins without any holes in the bottom. This reduces air supply to the bottom of the bin and allows moisture to accumulate there. I worry that these suboptimal conditions may cause harm to bugs that may get stuck in the bottom of the bin. But the alternative—in which lots of larvae and perhaps other invertebrates fall through the bottom holes of the bin—seems important to avoid.

Harvesting finished compost

When it comes time to harvest completed worm compost, worms and other bugs may be contained in this compost. If you immediately apply the compost to your garden, then these bugs will at least have somewhere to go. However, if you stick the completed compost into a bucket or seal it in a bag, the bugs stuck in the completed compost may suffocate, dry out, be crushed, or die of other causes. Wikipedia ("Vermicompost") mentions some methods for separating worms from their castings and says that the methods "differ on the amount of time and labor involved and whether the vermicomposter wants to save as many worms as possible from being trapped in the harvested compost."

Unfortunately, if you try to pick worms out of the finished compost by hand, then you'll crush lots of smaller invertebrates in the finished compost due to handling it so much. For this reason, I think the best way to harvest finished compost, if it must be done at all, is to wait until it's ready to be immediately applied to the garden and then grab chunks that contain as few worms as possible.

Violently controlling "pests"

I personally don't intentionally kill any invertebrates in my friend's worm bin, but some vermicomposters do. Numerous articles and forum discussions can be found about how to kill various unwanted invertebrates in compost bins. For example, Sherman and Bambara (1997-2011) review methods of "Controlling Mite Pests in Earthworm Beds", such as the following:

  • "Place pieces of watermelon or cantaloupe rind or potato slices on top of the worm beds. Mites are attracted to the sweetness of the rinds or peels and will accumulate on them. The rinds or peels can then be removed and dropped in water or buried."
  • "Use a hand-held propane torch to scorch the top of the bed and kill the mites."
  • "Use a light dusting of sulphur to kill the mites."

Ways I try to slightly reduce harm to invertebrates

Maintaining a worm bin involves inevitable harm to invertebrates, including direct harm to a small fraction of the decomposer animals. However, if a worm bin must be maintained, this section describes a few strategies I use to slightly reduce invertebrate suffering.

Fairly constant temperature

My friend's worm bin is kept in the basement. The basement is well insulated and has a water heater, which keeps the basement pretty warm during the winter. Meanwhile, since the basement is out of the sun and within the cool ground, it remains the coolest part of the house during the summer. In previous years, my friend kept the worms in a different part of the house that would occasionally freeze in the cold weather, which killed everything in the worm bin. I imagine that keeping a worm bin outdoors would also lead to temperature-control issues (and if the bin isn't covered, rain might drown bugs in the bin).

Collect food waste in a sealed container

I add food scraps to my friend's worm bin about once a week. In the meantime, food scraps are collected in a Cool Whip container or other plastic container with a sealable lid. If food scraps are collected in an open container, fruit flies are likely to infest it, which can result in a writhing mass of fly larvae in the food waste before it's even added to the worm-composting bin.

Should you bury new food waste?

Wikipedia ("Vermicompost"): "In warm weather, fruit and vinegar flies breed in the bins if fruit and vegetable waste is not thoroughly covered with bedding. This problem can be avoided by thoroughly covering the waste by at least 5 centimetres (2.0 in) of bedding." "What can be done" (n.d.) recommends the same and also suggests that one could "Freeze the food scraps overnight before adding them to the bin", presumably to kill fruit-fly eggs or larvae that the food scraps might already contain?

I sometimes bury new additions of food to the worm bin, and this sometimes does help reduce flies, although because the worm-bin humus can be clumpy, there are often cracks through which flies can still reach somewhat-buried food scraps. Even if I bury food scraps more than 5 centimeters within worm humus, I sometimes observe flies in the buried compost when I later dig around in order to add a new batch of food scraps. So it's not clear to me how successful burying of food scraps actually is, which makes me uncertain about whether this practice is net good or bad.

Since flies are smaller than earthworms, burying food waste might reduce the total number of invertebrates in your vermicomposting bin, since the same volume of food will be eaten by larger animals (worms rather than flies)? On the other hand, compost bins also contain tiny animals like nematodes, mites, and springtails, which are smaller than flies, so maybe burying food waste away from the reach of flies can increase populations of some of these tiny critters too?

A big downside of burying new food waste in the bin is that digging in the compost bin gets dirt on your hands, and as I've verified with my microscope camera, this dirt often contains tiny worms, springtails, and mites. Among the critters stuck onto your fingers, some will be fully or half crushed right away, and the rest will drown when you wash the dirt off into the sink. One idea for reducing the drowning part of this tragedy is to buy gloves that you wear when digging in the compost. This way, when the gloves get dirt on them, the critters in that dirt won't be drowned. However, if you leave the gloves in the compost bin, I imagine that lots of mites and springtails would wander into the gloves by the next time, in which case you might crush even more bugs when reusing those gloves. Therefore, the gloves should probably be stored away from the compost bin, but in that case, the bugs wandering off of them won't have food nearby. Also, even with gloved hands, digging in the bin still sadly crushes some invertebrates. Using a spoon to dig in compost is inadvisable because the spoon may cut worms in half.

If the springtail/mite population is particularly dense in your bin, then I imagine that digging in order to bury just a few food scraps could easily crush perhaps tens(?) of tiny invertebrates, depending on how crushable they are. This is a serious cost that should be weighed against the benefits of burying food scraps. (One benefit of burying food is that with fewer flies in the bin, fewer flies will be crushed in the future when you add new food.)

Minimizing disturbance when removing compost

A vermicomposting bin produces rich, dark humus at the bottom as the organic matter is broken down. My friend extracts this humus to use in a home garden. I insist that the humus be removed gently by hand by digging a hole in the compost and then grabbing the dirt from the bottom of the compost bin, as is shown in this picture. You can grab dirt from many parts of the bottom using a single central hole. Doing so minimizes disturbance to the invertebrates in the upper layers relative to other methods of extracting the bottom-layer humus. It would crush a lot more invertebrates to dump out the bin or to move all of the top-layer, undecomposed organic matter into a new bin. Also, keeping the worms in their current bin avoids the risk that they'll try to escape after being moved to a new bin whose conditions aren't yet to their liking.

I sometimes dig from a corner of the bin rather than the center so that my arm only brushes up against two sides of compost rather than four.

Use several bins simultaneously if necessary

My friend generates enough food waste for about two different large plastic containers. Theoretically you could add the waste all to one bin and then start using the second bin while the first one finishes decomposing. However, this might starve the worms in the first bin as the food supply dwindles. Instead I add food to one bin and then the other on alternate weeks. Finished compost can be harvested from the bottom of the bins even while fresh food is being added to the surface.

Adding as little organic matter as possible

While I have to add all my friend's food waste to the worm bin, I try to add as little other material as possible—usually just a few shredded newspapers from time to time. Probably the carbon:nitrogen ratio of my worm bin is lower than it's supposed to be because I add mostly food scraps rather than dry fiber, but I'd rather not increase the total mass of organic matter available for consumption, since this would presumably increase the invertebrate population. I suppose there's some chance that adding more shredded newspaper would make the compost sufficiently less favorable to invertebrates that the invertebrate population would actually decrease, but this seems unlikely to me.

Large-scale vermicomposting

While vermicomposting is often done on a small scale, Wikipedia ("List ...") reports that even large-scale, industrial composting operations may sometimes use vermicomposting, which is sad. Wikipedia ("Compost"): "Vermicomposting is widely used in North America for on-site institutional processing of food waste, such as in hospitals, universities, shopping malls, and correctional facilities." Wikipedia ("Vermicompost"): "Large-scale vermicomposting is practiced in Canada, Italy, Japan, India, Malaysia, the Philippines, and the United States."

Yeager (2011) reports on "Worm Power’s worm composting facility in upstate New York", which is "the largest vermicomposting facility in the Western Hemisphere." "Inside worm beds that would stretch from one football sideline to the other, 15 million worms are hard at work." Before being fed to worms, the organic matter is briefly composted at high temperatures, which I assume kills any invertebrates that might have been present in the input materials. "the feedstock undergoes thermophilic (high-temperature) composting in indoor, aerated static piles. The piles must reach a temperature between 131° F and 170° F for a minimum of three consecutive days. These high temperatures kill potential pathogens in the compost, deactivate weed seeds, and produce a feedstock that worms can digest readily."