by Brian Tomasik
First published: 12 Jan. 2018; last update: 12 Jan. 2018

Summary

This page discusses the invertebrates brought into existence by different forms of home composting and large-scale composting. My general impression is that non-hot aerobic composting (such as vermicomposting) creates the most invertebrates per unit of food decomposed, and therefore, such systems also create the most invertebrate suffering and death per unit of food decomposed. Hotter or less aerobic composting systems seem likely to produce fewer invertebrates. Many large-scale composting operations reach high temperatures and so probably create somewhat fewer invertebrates per unit of food decomposed than many small-scale composting operations, though large-scale compost piles still do contain lots of nematodes, flies, etc. in cooler phases. Instead of composting, I recommend other methods of food-waste disposal.

Epigraph

Steel and Bert (2011), p. 46:

The mesofauna of compost includes Isopoda, Myriapoda, Acari, Collembola, Oligochaeta, Tardigrada, Hexapoda and Nematoda. This wide spectrum of organisms forms a complex and rapidly changing community that is not limited to a specific compost but can be found from vermicompost to mushroom compost and from small- to large-scale controlled or open-air composting processes.

Introduction

Decomposition of food scraps and other organic wastes in low-temperature, oxygen-rich composting systems is likely to breed large numbers of invertebrates, including earthworms, beetles, flies, springtails, mites, and nematodes. These animals are born without their consent into short lives that end with potentially painful deaths. For this reason, I think it's morally important to reduce the number of invertebrates who are created by food-waste disposal.

This piece examines how many invertebrates are created by various methods of composting. Because I'm not an expert and it's hard to find explicit data on invertebrate densities in different composting systems, the generalizations in this article should only be considered qualitative best guesses.

Home composting piles

Seeker (2014) shows a simple compost pile built in a plastic container whose bottom has been cut off. New food scraps are buried within the pile. It's suggested to aerate the pile by mixing it about every week. While the video doesn't discuss the topic, I would guess that such a bin would attract flies and other invertebrates.

Stuff You Should Know (2017) (at 17m25s) discusses building a compost container out of chicken wire: "Build a wood frame and it's got chicken-wire walls and a chicken-wire bottom. And that gets you the air." Such a structure would allow flies and probably other bugs to enter.

University of Illinois Extension ("Composting Methods") shows a number of methods of home composting. My inference based on the descriptions of these methods is that basically all of them allow at least flies to access the compost, or, if the compost is buried, then soil invertebrates can access it.

Olynciw (1996): "In outdoor compost piles, a wide range of invertebrates take part in the decompos[i]tion of organic matter."

Trautmann (1996) enumerates a variety of types of invertebrates that may inhabit "small-scale outdoor composting systems, such as backyard compost piles". I won't reproduce the list here, but it's interesting to read. Nematodes "are the most abundant of the physical decomposers - a handful of decaying compost contains several million." (This nematode numerosity estimate seems somewhat high relative to estimates discussed later in this piece in the "Steel et al. (2013)" and "Steel et al. (2010)" sections.)

Aggie Horticulture (2009):

By far the most important microscopic decomposers are bacteria, which do the lion’s share of decomposition in the compost heap. But there are other microscopic creatures such as actinomycetes, fungi, and protozoa, that also play an important role. [...] The larger fauna in the heap include mites, millipedes, flatworms, centipedes, sowbugs, snails, slugs, spiders, springtails, beetles, ants, flies, nematodes and, most importantly, earthworms.

Aggie Horticulture (2009) goes on to provide the following quote from Daniel L. Dindal's Ecology of Compost:

mites and springtails eat fungi. Tiny feather-winged beetles feed on fungal spores. Nematodes ingest bacteria. Protozoa and rotifers present in water films feed on bacteria and plant particles. Predaceous mites and pseudo- scorpions prey upon nematodes, fly larvae, other mites and collembolans. Free-living flatworms ingest gastropods, earthworms, nematodes and rotifers. Third level consumers such as centipedes, rove beetles, ground beetles, and ants prey on second level consumers. These creatures function best at medium or mesophilic temperatures, so they will not be in the pile at all times.

As the last sentence of this quote hints, compost piles can sometimes get hot, which I discuss next.

Hot temperatures kill invertebrates

Home compost piles sometimes get hot on the inside, perhaps even hot enough to kill invertebrates? This might be good insofar as it reduces invertebrate populations, although dying of overheating is probably very painful for invertebrates.

Trautmann and Olynciw (1996) explain: "Under optimal conditions, composting proceeds through three phases: 1) the mesophilic, or moderate-temperature phase, which lasts for a couple of days, 2) the thermophilic, or high-temperature phase, which can last from a few days to several months, and finally, 3) a several-month cooling and maturation phase." Trautmann and Olynciw (1996) present a graph of temperature over time in which, according to my eyeballing of the graph, the compost pile starts out around ~20°C (~68°F), increases to ~55°C (~130°F), and eventually drops to ~25°C (~77°F).

University of Minnesota Extension (n.d.) says regarding home compost piles: "To prevent odors and hasten decomposition, the pile should be turned occasionally. Turning also exposes seeds, insect larvae, and pathogens to lethal temperatures inside the pile. [...] An actively decomposing pile will reach temperatures of 130-150 degrees F in the middle."

University of Illinois Extension ("Composting Methods"): "Higher temperatures produced as a result of turning (90° - 140° F) will kill major disease organisms and fly larvae, help kill weed seeds, and provide a good environment for the most effective decomposer organisms."

University of Illinois Extension ("The Science ..."): "Thermophilic temperatures kill fly larvae."

Trautmann (1996): "Flies spend their larval phase in compost as maggots, which do not survive thermophilic temperatures."

Aggie Horticulture (2009): "Compost piles under aerobic conditions attain a temperature of 140°F to 160°F in one to five days depending upon the material and the condition of the composting operation. [...] A well-mixed, adequately working compost pile will heat to temperatures between 110°F and 160°F as the microbes actively feed on the organic materials. [...] Fly larvae will not survive the thermophilic temperatures in the well-managed compost pile." Aggie Horticulture (2009) enumerates a variety of types of invertebrates that act as "physical decomposers" and explains that "Most of these creatures function best at medium or mesophilic temperatures, so they will not be in the pile at all times." Regarding ants, Aggie Horticulture (2009) explains that compost "provides shelter for nests and hills. They will remain, however, only while the pile is relatively cool."

Wikipedia ("Hot container composting") explains that composting within an insulated container can keep compost hot—in contrast to a cold compost pile, which "Attracts flying insects, e.g. flies". (Does hot-container composting have few flies because of the heat or because the container is sealed, or both?)

CalRecycle (2012) explains that earthworms "prefer the pile when it is cooler, so adding worms could lead to their quick demise in a hot, steamy pile."

Even if the thermophilic phase of decomposition in home compost piles is too hot for invertebrates, are invertebrates present during the later phases? Aggie Horticulture (2009) says "There are many organisms that breakdown organic materials. Most are not seen by the human eye, but they are there throughout the process. Others that are large enough to see, are usually associated with the later breakdown stages." Assuming these organisms "that are large enough to see" are invertebrates, it seems that invertebrates do colonize compost piles in the later stages of decomposition.

Steel et al. (2013), p. 108: "Nematodes are omnipresent in composts and are active in virtually all stages of the composting process. Major shifts in species composition, life strategies, and feeding behavior occur during the composting process. Due to the heat peak, nematodes can be virtually absent, but several taxa appear immediately when the temperatures drop."

Aggie Horticulture (2009) says: "Except in the final stages of the composting period, when the temperature drops, actinomycetes and fungi are confined to a sharply defined outer zone of the stack, 2 to 6 inches in thickness, beginning just under the outer surface. [...] The sharply defined inner and outer limits of the shell (in which actinomycetes and fungi grow during the high temperature active composting period) are due to the inability of these organisms to grow at the higher temperatures of the interior of the pile." So it sounds like even during the thermophilic phase, the exterior of the pile remains cooler.

Are small-scale composting operations thermophilic?

I conjecture that real-world home compost piles might not become thermophilic if decomposition occurs slowly or if a pile has a high surface-area-to-volume ratio.

Composting in the Pacific Northwest (2009a) discusses compost-pile temperatures (in °F) in a podcast (10m57s): "The best range is like mid-80s to mid-120s, but we want it to get to 130. We want it to peak and we want to kill weed seeds. But what's likely going to happen is you're going to poke around and you'll find a hot spot that'll be 130 or 140, but the outside will only be 70 or 80 or something."

Chardoul et al. (2015), p. 2-6: "Smaller scale composting (i.e. backyard composting) rarely achieves high enough temperatures to effectively kill weed seeds and pathogens." And University of Illinois Extension ("The Science ...") says that high temperatures are often not required for amateur composters: "While high temperatures (above 140º F) have the advantage of killing pathogenic organisms and weed seeds, it is unnecessary to achieve those temperatures unless there is a specific concern about killing disease organisms and seeds."

Composting done by spreading organic material over a large area, such as leaving mowed grass or fallen leaves to decompose in place, doesn't generate high temperatures, and such decomposition is likely to involve lots of invertebrates. Steel et al. (2013) note (p. 108): "In nature, the mineralization of organic matter is a slow process that does not produce a recognizable heat peak (Kutzner 2000)."

Turning the compost

Compost piles are supposed to be turned regularly to provide air, as well as to make moisture and temperature more uniform. Unfortunately, mixing is likely to crush some invertebrates, such as flies that may inhabit the surface of the pile. I suspect that crushing bugs is bad because the crushed bugs will plausibly endure painful deaths, but the overall bug population is not appreciably reduced by killing a few of them, so presumably the bugs you kill will soon be replaced. (This is in contrast to killing basically all invertebrates in a compost pile for a period of time during a thermophilic composting phase. During the thermophilic period, a lot of decomposition occurs without any invertebrate involvement. Still, I do worry that the pain of heating bugs to death when a compost pile becomes hot might be a pretty big downside to thermophilic composting. The best solution is to avoid aerobic, invertebrate-filled composting altogether.)

Home vermicoposting

See "Invertebrate Suffering Caused by Worm Composting".

Other aerobic home-composting methods

Rotating containers

Rather than having compost pile up on the ground, people sometimes compost within a rotating container. The top non-Sponsored result on Amazon for the query {composter} is, as of Oct. 2017, "Yimby Tumbler Composter". The product information explains: "Avoid digging and mixing your compost pile by hand. The tumbling design makes mixing easy and efficient. Just close the door and turn it 5-6 times every 2-3 days." Unfortunately, all this tumbling is liable to crush flies that may inhabit the composter. And the composter does indeed attract or breed flies, as we can see from product reviews. Here are a few quotes from various reviews:

  • "the flies were fairly bad this summer."
  • "A few weeks after we started putting kitchen scraps in one side, I noticed the contents were writhing with big larvae. Looked them up online and found out my tumbler had attracted black soldier flies. I have seen the big flies themselves entering into the tumbler by the few small slits/ ventilation holes all around the right and left sides of the tumbler."
  • "Black Soldier Flies found their way in and I didn't have to do anything! The holes for aeration allow tiny creatures to enter and exit".
  • "It attracts flies and maggots and ants, but that doesn't hurt the process."
  • "be prepared for more fruit flies than you'd like."
  • "Rodents definitely can't access the material, but flies and mosquitos were rampant."

Epic Gardening (2016) shows flies and fly larvae in a Yimby Tumbler Composter. The flies can enter the various air holes in the tumbler.

Green Cones

Martinko (2016): "The Green Cone, which is made of plastic, has a cone-shaped top and an attached basket that gets buried underground below the cone. You dump food scraps into the top, via a hinged lid, and they fall down into the basket. There, the food waste is broken down and consumed by bacteria, fungi, microorganisms, worms, and insects."

A composting expert in Composting in the Pacific Northwest (2009b) explains (2m55s): "No need to add worms. They will migrate in from the outside in. But they're not really the primary decomposers at work. It's more the microorganisms and the beneficial fungi and bacteria that are doing most of the work in there." Unfortunately (4m19s): "In the summer you can count on having some fruit flies in there."

Earth Machine

enviromompdx (2008) shows an "Earth Machine"—a barrel-sized cylinder where food goes in the top and compost comes out the bottom. I assume that bugs can get in through ventilation slits?? ORBIS Corporation (2012) says: "During the summer, you may be greeted by fruit flies when you open your Kitchen Collector or Earth Machine™. To keep them at bay [...] At your Earth Machine™, add leaves or a thin layer of soil each time you add fresh material." Of course, adding this layer may crush some fruit flies.

Barrels

Rob Palmer DIY (2016) shows a compost barrel full of maggots, who are violently killed by adding lime and stirring aggressively. Even after the large maggots have been killed, you can see a few small invertebrates remaining in the compost (2m22s).

Steel et al. (2013)

Steel et al. (2013) examined "nine compost barrels[...] in a garden in Heusden, Belgium [...]. The barrels had a total volume of 290 L each (height=96 cm, upper diameter=52 cm and lower diameter=80 cm)" (p. 109). The composition of the compost was as follows (p. 110):

All barrels were filled with the same amount of feedstock materials on a volume-to-volume base (v/v): 38% (v/v) of pure wood chips (mainly boxwood [Buxus sp.] and young willow twigs [Salix sp.]) and 62% (v/v) of a homogenous mixture of 55% fresh grass and 45% mixed wood chips. The compost in the barrels was mixed once, on day 7, during the thermophilic phase.

Following is a list, taken from supplemental Table S1, "of the arthropod taxa whose members were captured in the compost barrels during the course of the experiment", using either pitfall traps or sticky strips (p. 119). Based on Wikipedia, I added common names in parentheses.

  • Acari (mites)
  • Anisopodidae (wood gnats)
  • Anthicidae (ant-like flower beetles)
  • Calliphora vicina (blue bottle fly)
  • Chironomidae (nonbiting midges)
  • Chrysomelidae (leaf beetles)
  • Collembola (springtails)
  • Coccinellidae (ladybird beetles)
  • Cynipidae (gall wasps)
  • Dolichopodidae (long-legged flies)
  • Drosophila sp. (small fruit flies)
  • Dytiscidae (predaceous diving beetles)
  • Formicidae (ants)
  • Hybotidae (dance flies)
  • Ichneumonidae (a parasitoid wasp family)
  • Monotoma picipes (a type of beetle)
  • Muscidae ("some [...] are commonly known as house flies or stable flies")
  • Phoridae ("small, hump-backed flies resembling fruit flies")
  • Psilidae (rust flies)
  • Sarcophagidae (flesh flies)
  • Scatopsidae (minute black scavenger flies)
  • Sciaridae (dark-winged fungus gnats)
  • Sphaeroceridae (small dung flies)
  • Sphecidae (a "family of parasitoidal wasps")
  • Staphylinidae (rove beetles)
  • Syrphidae (hoverflies)
  • Tenthredinidae ("largest family of sawflies")
  • Coleoptera (beetle) larvae
  • Muscidae ("a family of flies") larvae
  • Diptera (fly) larvae
  • Stratiomyidae (soldier fly) larvae.

Steel et al. (2013) also reported (Fig. 6, p. 115) the following densities of nematodes in the nine compost barrels, where the x axis is days of the composting process and the dotted/gray/black lines represent three variations of the composting barrels. "DW" means "dry weight".



Burying food waste

enviromompdx (2008) proposes as one home-composting method to bury food scraps in a hole in the backyard. The video explains an advantage of this method for the humans doing the composting (2m49s): "There's no smell or flies; the worms and microbes do all the work underground." Does burying food scraps create fewer or more total invertebrates than composting aboveground? It's also worth noting that digging holes can sometimes chop earthworms in half, and the pressure of a shovel or your digging fingers may crush smaller soil fauna.

University of Illinois Extension ("Composting Methods") describes two methods of composting in the ground:

  1. "Sheet Composting": "Sheet composting involves spreading a thin layer of organic materials, such as leaves, over a garden area. The materials are then tilled in with a hoe, spade, garden fork, or rotary tiller." This method is slow and not thermophilic, so presumably invertebrates contribute to the decomposition.
  2. "Pit or Trench Composting": "Dig a one-foot-deep hole. Chop and mix the food wastes into the soil then cover with at least 8 inches of additional soil."

Anaerobic composting

Invertebrate animals generally require oxygen for respiration. Anaerobic conditions tend to lead to domination by organisms that are less cognitively sophisticated than animals and hence who plausibly suffer less per unit of metabolism performed. Landfilling is one form of (mostly) anaerobic "composting".

Bokashi composting

Bokashi composting is a form of anaerobic fermentation, and unlike landfilling of organic wastes, it doesn't appear to generate significant methane or other gases (Footer 2014, p. 13).

Footer (2014): "Because you are fermenting organic matter anaerobically in a closed system, not composting it in the traditional sense of the word," there are "No insect or rodent issues" (pp. 7-8). Bokashi Composting Australia (2014) adds: "The bokashi bucket has an airtight lid so there are no smells and it won’t attract any insects."

While this sounds ideal from both a traditional environmentalist perspective and from the perspective of reducing invertebrate suffering, the problem is that, as far as I can tell, fermented Bokashi compost may feed lots of bugs once it's added to garden soil. If few gases are emitted (is that actually true?), then most of the carbon and nutrients must remain in the end product, and I assume this material will eventually be eaten by soil organisms, including soil invertebrates? Footer (2014): "A lot of carbon is lost in the traditional composting process" due to respiration (p. 14). But "By fermenting waste in a closed container without producing CO2, you are putting the carbon and other organic materials directly into the soil when you use the bokashi pre-compost" (p. 14).

Does this bokashi pre-compost feed lots of soil invertebrates? Apparently yes:

  • Gardens from Garbage (2010): "Worms, insects, and other beneficial microbes finish the process of digestion after the [bokashi] contents are added to the soil."
  • Bokashi Composting Australia (2014): "When bokashi waste is buried, along with the carbon and nutrients produced by the fermentation process you are also adding Bokashi mix which is full of millions of beneficial micro-organisms. These microbes significantly accelerate the breakdown of the waste. This method [...] promotes earthworms", among other things.
  • The Compost Gardener (n.d.): "while the acidity of bokashi eliminates fruit flies, rodents, and pathogens you might be worried that it is going to make your soil acidic. Tests show that the bokashi neutralizes completely during the burial part of the process. Once neutral it also becomes a favorite food for earthworms."

My impression is that Bokashi is basically a fancy pre-processing step added to the simpler method of composting food waste by burying it.

Footer (2014) notes that "When you compost using bokashi", the microorganisms "go to work consuming sugars from the organic waste and the fermentation process begins" (p. 8). So it sounds like at least some of the food energy in the waste is at least partly eaten before the waste is applied to the garden. However, Gardens from Garbage (2010) explains regarding organic matter in a Bokashi bucket: "The color and shape does not change in an airtight bucket because the food waste is fermented anaerobically." This suggests to me that not much of the food energy in the organic matter is consumed prior to adding the fermented waste to the garden? In other words, not much of the food energy is eliminated in invertebrate-free conditions? EachOneTeachOneFarms (2011) shows burial of Bokashi-fermented food waste and says (4m14s): "You can see everything still looks pretty much the way it looked in its past life. Again, remember we are pickling our waste. Just like a pickle still looks like a cucumber, so does our waste. It's not until we bury the stuff in the ground that [...] the microbes in the soil finish off that decomposition process".

Since at least a little bit of the Bokashi-composting process is anaerobic, maybe Bokashi composting creates slightly less invertebrate suffering than just burying food waste directly? On the other hand, the Bokashi process requires adding some external carbohydrates ("Bokashi Bran"), such as wheat bran and molasses (TeraGanix 2014), which might increase the total volume of organic matter that you have to compost and the total amount of buried food available to invertebrates?

While the basic Bokashi process is not in dispute, some of the claims made by practitioners about special "effective microorganisms" have not been rigorously verified (Wikipedia "Effective microorganism").

Large-scale composting

Chardoul et al. (2015) is a guidebook for "Commercial Scale Composting Operations". It includes the following general comment about invertebrates in composting, though it's not clear to me if this statement applies to large-scale composting specifically: "Composting is a process carried out primarily by microorganisms that decompose organic materials. The major groups of microorganisms that are active during composting are bacteria, actinomycetes, and fungi. Other organisms that complete the diversity of decomposers include nematodes, protozoa, and micro-arthropods. In the visible spectrum are earthworms, arthropods, larger nematodes, beetles, and other detritus eating insects" (p. 2-3).

Temperatures

In many large-scale composting operations, the compost piles reach high temperatures:

  • Eco-Products (2014) suggests that in large-scale composting, the compost pile can warm to 131 to 160°F (1m23s).
  • Compost Turner (n.d.) says regarding industrial composting: "Most commercial facilities regularly turn or aerate their piles and monitor the internal temperature to assure it is between 105°and 145°F."
  • Blanchard (2015) is a podcast interview with Karl Hammer of the Vermont Compost Company. At Vermont Compost, one composting stage that involves chickens can be ~95-100°F (59m48s), while the subsequent thermophilic stage reaches 131-140°F (60m22s).a Vermont Compost Company (2016) reports the thermophilic temperatures as in the range 131 to 145°F for at least two weeks (1m56s).b
  • Hammond Farms Landscape Supply (2017) reports that their windrows reach "internal temperatures of 140 to 160°F" (1m52s).
  • Composting in the Pacific Northwest (2010), describing a company that does large-scale composting: "Cedar Grove is cooking their stuff at about 180°F" (6m38s).

I would guess these temperatures are often too hot for invertebrate animals? Are the temperatures cooler on the surfaces of the piles, allowing invertebrates to live there?

Chardoul et al. (2015) offer an idealized graph of temperature over time for windrow composting (p. 2-4):

Can animals infest the compost piles at non-thermophilic stages of the composting process? At least for nematodes, I think the answer is "yes", as discussed below.

Nematodes

Steel et al. (2010)

Steel et al. (2010) measured nematodes during a large-scale composting process. "The examined compost heap was located at the Institute for Agricultural and Fisheries Research in Merelbeke, Belgium [...]. The heap was composed of three different feedstock materials: 43% fine wood chippings, 43% dry hay and 14% fresh grass. [...] The heap was 50 m long, 3 m wide and 1.5 m high" (p. 182). The results (Fig 2a, p. 185):

The authors explain (p. 185):

Immediately after the heat peak, on day 3 until day 9, nematodes could not be detected, except for H. gingivalis and D. coronatus[...]. Thereafter, the number of nematodes increased gradually until the final sampling event. The highest numbers of nematodes were found in the first and in the last samples (respectively, 1234 and 933 nematodes per 100 g dry weight compost).

The peak nematode abundances were roughly ~103 per 100 g dry compost or ~101 per g dry compost. That number is comparable to typical nematode densities in regular soils according to Brady (1974), who reports nematode numbers in surface soils as between 101 and 102 per gram of soil. (I'm not sure if Brady (1974)'s numbers are for wet or dry soil.)

Steel et al. (2010) offer a caveat on their nematode counts: "The abundance (individuals/gram dry weight compost) of each genus or species in each sample was determined. Dauer larvae were not included in the total counts and species analysis because accurate identification is often impossible and the[ir] immobility hampers a quantitative estimation using a mobility-based nematode extraction" (p. 182).

I wonder if some composting operations finish before the late stages when nematode numbers increase a lot? For example, based on the above graph, if the compost were harvested at around 110 days, there would only be ~1 nematode per gram of dry compost. This is still a nontrivial number. Plus, the compost would contain undecomposed organic matter that could continue to degrade when applied to farm fields, thereby possibly feeding further nematodes and other invertebrates.

While all nematodes in compost die in one way or another, some nematodes endure death by predation. Steel et al. (2010) report: "The composition of nematode feeding types showed a clear dominance of bacterial feeders (16 species or 55% of the total abundance), followed by the subdominant fungal feeders (5 species or 33.3% of the total abundance) and the bacterial-feeding and predatory (of nematodes) nematodes (2 species or 11.7% of the total abundance)" (p. 185). And "This study shows that a composting process can provide a great range of potential predator nematodes" (p. 188).

Flies

Chardoul et al. (2015) say (p. 8-10):

Flies and other pests such as gnats, rodents or other small wildlife are attracted by the odor of decomposition, and need to be controlled for public health and aesthetic reasons. Flies may deposit their eggs on the compost and the warm, moist conditions just below the surface provide an ideal environment for their larvae. While pests may become a problem at any compost facility, they are often a sign of a poorly managed site. Process control and good housekeeping can limit both the number and impact of pests.

Goulson et al. (1999) compared fly abundances at various locations, including two composting sites and a landfill. The results (p. 493): "Very large fly populations were found at the two composting sites, and it seems likely that these provide ideal breeding grounds for a range of fly species since they offer an abundance of warm decaying organic matter." That said: "Large fly populations were also evident at the landfill site."

KQED (2011) shows (2m3s) compost windrows covered with a tarp. Does this help keep flies out?

Shredding and mixing

Large-scale processing of compost involves several steps where, if invertebrate animals are present, some of them are probably painfully crushed, suffocated, or overheated.

"Hamilton ..." (2006) explains (p. 5) that at the Hamilton Centralized Composting Facility, the "Process Flow" includes, among other steps, "Mixing of materials" and "Shredding" prior to composting. I assume these steps injure invertebrates that may be present in the input organic matter.

Hammond Farms Landscape Supply (2017) explains that "Coarse, heavy materials like logs and brush are fed into our high-powered horizontal grinder to reduce their size. Then they will be mixed with other materials like leaves, grass, and food scraps in composting windrows to begin the process" (1m30s). Plus, once the windrows are built, "Over the following four months, the rows are turned two to three times per week with a windrow turner" (1m58s). I assume all these steps can injure and kill invertebrates.

Chardoul et al. (2015) say (p. 8-10) "it is essential to [...] kill fly larvae by frequent turning."

I wonder if post-processing and bagging compost for sale to end users harm invertebrates that are in the compost? Do the invertebrates dry out or suffocate in the compost bag while waiting to be sold on store shelves?

Windrow vs. Aerated Static Pile

Compost site GermanyReFED (2016) explains: "In rural areas, [composting] can be accomplished by periodically turning large piles, or windrows, of organic waste over themselves using specialized equipment. In more urban areas, Aerated Static Pile (ASP) composting is generally preferred, where piles can be covered and mechanically aerated in order to minimize the site’s footprint and odors." Intuitively I would guess that ASP composting is better than windrow composting because fewer bugs can get into the compost piles in ASP systems? Also, since the piles don't need to be turned over, bugs aren't crushed and heated to death in that process.

Wikipedia ("Aerated static pile composting") explains that ASP compost "may be in windrows, open or covered, or in closed containers. [...] ASP facilities can be under roof or outdoor windrow composting operations, or totally enclosed in-vessel composting, sometimes referred to tunnel composting." Wikipedia ("In-vessel composting") explains: "In-vessel composting generally describes a group of methods that confine the composting materials within a building, container, or vessel."

Misra et al. (2003) review several methods of large-scale composting. Except for methods done fully indoors, it seems to me like most of these composting processes allow flies to access the piles? For the "Passively aerated wind-rows" and "Aerated static pile" methods, the authors mention that covering the piles with a layer of compost, peat, or bulking agent "discourages flies".

Diggelman and Ham (2003) report regarding the Columbia County, Wisconsin Composting Facility: "It is assumed that 83% of the decomposition occurs in the in-vessel composter and 17% occurs during the windrow curing which follows" (pp. 509-10).

Mushroom compost

The "Mushrooms" section of Tomasik ("Vegans ...") includes some discussion of flies that are associated with large-scale composting for commercial mushroom production.

Beyer (2017) describes commercial mushroom production, including preparation of mushroom compost. "The use of forced aeration, where the compost is placed on a concrete floor or in tunnels or bunkers and aerated by the forced passage of air via a plenum, nozzles or spigots located in the floor has become nearly universal in the mushroom industry". Beyer (2017) explains that the first phase of composting can get very hot: "Temperatures in the compost can reach 170° to 180°F during the second and third turnings when a desirable level of biological and chemical activity is occurring." After the first phase of composting is done, "Pasteurization is necessary to kill any insects, nematodes, pest fungi, or other pests that may be present in the compost." So it appears that large-scale compost piles may contain at least some insects, nematodes, etc., even though such piles can get very hot. Are there just a few stray flies/nematodes/etc. that happen to make their way to the compost pile as it's cooling down, or do large populations of invertebrates grow within the pile?

While composting for mushroom production creates some invertebrates, my guess is that the organic wastes would typically decompose aerobically even if they weren't intentionally composted?? If so, that decomposition would also create lots of invertebrates. It's plausible that large-scale composting creates fewer invertebrates per unit of organic matter decomposed than small-scale composting or natural decomposition does because large-scale composting is more likely to be thermophilic.

Beyer (2017) reports: "Two types of material are generally used for mushroom compost, the most used and least expensive being wheat straw-bedded horse manure. Synthetic compost is usually made from hay and wheat straw". Whether composting such materials creates more or fewer invertebrates than the alternative disposal method depends on the alternative disposal method. For example, if manure would otherwise be decomposed anaerobically, and if plant fibers would otherwise be burned, then composting plausibly creates more invertebrates, in which case mushroom farming is somewhat bad from the perspective of invertebrate suffering. On the other hand, if the manure would be composted anyway, and if the plant fibers would be left to decompose on pastures or crop fields, then thermophilic composting of those materials probably creates fewer invertebrates, in which case mushroom farming would be slightly good from the perspective of invertebrate suffering (assuming that the pain that invertebrates experience when heating to death in a thermophilic compost pile isn't so severe as to outweigh the reduction in suffering due to having fewer total invertebrates exist in thermophilic composting compared with lower-temperature aerobic decomposition).

A note on original sources

While researching this piece, I noticed that many pages describing compost invertebrates contained roughly the same content and roughly the same language as one another. In some cases there appeared to be straight copying and pasting of text without attribution. For example:

  • Try Googling the following quote from Aggie Horticulture (2009): "provides shelter for nests and hills. They will remain, however, only while the pile is relatively cool." The quote appears in several sources, and it looks like the earliest is probably The Rodale Book of Composting, published in 1992.
  • Try Googling the following quote from CalRecycle (2012): "Sow bugs are fat bodied crustaceans with delicate plate-like gills along the lower surface of their abdomens". Once again, many different pages are returned, including Trautmann (1996).

I haven't checked all the sources I cited or quoted in my piece to see if they copy-pasted text from other sources, but I thought it was worth at least mentioning this phenomenon.

Footnotes

  1. As an aside, Hammer mentions that his composting operation takes in bark that might otherwise be burned (75m18s). This probably increases invertebrate suffering because composting bark creates lots of invertebrates, while burning bark doesn't. Of course, burning bark is probably painful for whatever invertebrates might occupy the bark when it's burned.  (back)
  2. In the same video, you can see lots of flying insects on compost at 1m15s, 1m40s, and 3m46s.  (back)