by Brian Tomasik
First written: 16 May 2015; last update: 24 Dec. 2016

## Summary

Most insects die soon after birth, and their lives probably contain more suffering than happiness. If you have a lawn that you actively maintain, you should consider converting your grass to hard landscape materials like gravel, or to artificial turf, to reduce plant biomass and therefore insect suffering. This could save you labor in the long run, reduces your probability of tick bites, and may be good for the environment. It may prevent at least hundreds of insects from suffering per dollar and might even save you money. However, if you don't actively manage your lawn, the calculation becomes less clear because eliminating a grass lawn might slightly contribute to climate change.

Note: I assume that in many places, neighborhood rules or building codes might prevent you from replacing a lawn with gravel. Would artificial turf be acceptable? Also, maybe it would be allowed to at least put a strip of rocks around the perimeter of your home, or something like that? Doing so might also slightly reduce the number of insects that come indoors. Finally, when picking out a house, you can consider gravel-friendliness as one factor. Other things being equal, it seems better to choose a house in a more rural area where you can buy a larger amount of more secluded land.

If you can't use gravel, you could consider adding a porch or other structure that would cover some grass, although the amount of land covered per unit cost might be small.

## Motivation

It's often claimed that there's nothing humans can do to reduce the suffering of insects in the wild. This claim is wrong. One important way to help wild insects is to study the effects of human environmental policies on insect populations and favor those policies that cause fewer insects to come into a nasty, brutish, and short existence. This work is important but involves a high degree of uncertainty in the analysis.

If you actively manage your lawn, then a relatively clear-cut way to reduce insect suffering is to replace your lawn with non-biological materials in order to prevent plants from growing. The reason to focus on eliminating plants is because plants are the "roots" of the food chain. As long as plant energy is created, someone is eventually going to eat it (whether insects, bacteria, or other critters). So just shuffling around population dynamics for heterotrophs isn't solving the fundamental problem that more plant energy means more life. Preventing photosynthesis stops the problem before it gets started.

## Material types and costs

Converting grass lawns to gravel, glass, artificial grass, or other materials is a common landscaping practice -- one that many people do without giving a thought to insect suffering. You can find tons of articles by searching {gravel landscaping} and similar queries. This page has a slideshow of options.

Another page gives prices for different materials:

 Type Price Decomposed granite $35 to$50 per cubic yard Pea gravel at least $33 to$50 per cubic yard River rocks $100 to$700 per ton Crushed granite gravel at least $60 per (cubic?) yard The cost to install a square foot of pea gravel is$1.1 to $1.8. Another source reports$1-$3 per square foot. Artificial grass costs$5 to $20 per square foot. ## Gravel costs vs. lawn-care savings The average lawn in the US is about 0.2 acres, or ~8700 square feet. Assuming$1-$3 per square foot, the cost of converting your lawn to gravel would be ~$9K to ~$27K. Once converted, you can avoid the costs of mowing, watering, etc. This page estimates$800-$1000 to pay for lawn-mowing services per year. If you do the mowing yourself, say it takes 10 hours per year at a cost of$50/hour, or $500. Assume a discount rate of 5% and that the gravel lawn lasts 20 years. Saving$500/year for 20 years has a present value of $500 * (1-1.05-20)/(.05/1.05) =$6,500. Saving $1000/year has a present value of$13,000. So a gravel lawn might or might not pay for itself. Of course, this calculation also depends on how a non-grass lawn affects your home price relative to a grass lawn, whether gravel is allowed by local regulations, etc.

If converting to gravel saves you money, that's great. Even if it doesn't save you money, it might be worth doing anyway depending on its cost in order to reduce insect suffering. How much insect suffering it reduces is the topic of the next section.

## How many insects are helped?

All told, the Earth has about 13.4 billion hectares of land. Your 0.2-acre lawn is about 6*10-12 of the total. If the world's 1018 insects were distributed evenly across the Earth, your lawn would contain ~6 million insects. This estimate seems too high, because tropical regions of the world house a disproportionate share of insects (although Arctic and Antarctic regions contain disproportionately fewer insects).

This discussion estimates insect densities on farm land as ~10 million per hectare, or ~4 million per acre. That again seems plausibly too high for lawns. Indeed, sometimes I don't see any bugs on lawns, though at other times I see lots of little critters hopping around. But lawns definitely are home to bugs.

A slightly lower estimate of how many insects live on lawns at a given time or are later supported by the biomass produced on lawns (e.g., decomposers eating dead grass clippings) at a given time might be -- just making up a number based on personal observation -- 5 per square foot.a Assuming a lawn of 0.2 acres, that implies ~44,000 insects supported by your lawn's grass at any given time. Grass biomass also supports tons of bacteria, nematodes, etc. (especially when it decomposes). Suppose these collectively matter as much as all the insects. Then your lawn supports a total of 44,000 actual insects + 44,000 equivalent insects = 88,000 "effective insects" at a given time during the non-winter months. (The appendix at the end of this piece estimates a similar, though slightly higher, number of effective insects using an alternate approach.) Making the conservative assumption that these insects go through one generation per year, then you prevented 88,000 effective insect deaths per year. And if the gravel lawn lasts, say, 20 years before needing to be redone, that's 88,000 * 20 = ~1.8 million effective insects saved from a short life and miserable death. And this ignores the fact that many of those insects would give birth to hundreds of baby insects, most of which would die soon after being born. So the actual number of insect deaths prevented may be many times higher.

## Comparison with humane insecticides

Gravel lawns and humane insecticides are both concrete ways to reduce insect suffering. I look more favorably on gravel lawns because

• there's less risk of a gravel-lawn campaign being misinterpreted to imply something possibly harmful, whereas a campaign to reduce the pain of insecticides might lead most casual observers to wrongly assume that we're in favor of organic farming
• pending more thorough research on how much lawns sequester carbon, promoting gravel lawns seems to have low uncertainty and doesn't rely on assumptions about the run-on ecosystem effects of a different insecticide or whether one type of insecticide is really more humane and equally lethal compared with another
• the start-up costs of a gravel-lawn campaign are smaller (all that's required is to promote something that some people already do)
• people might look more favorably on gravel lawns, considering that, e.g., they help with California's droughts and might reduce climate change
• the case for gravel lawns more prominently brings up the idea that bug lives in aggregate have more bad than good.

The main reason why humane insecticides might have higher payoff is that in the long run, it might be possible to help more insects more cheaply if humane insecticides became widespread, since the dollar cost per hectare affected per year is probably smaller for humane insecticides. But given that most people oppose insecticide use for reasons of human and environmental health, I doubt there could ever be a widespread movement with economies of scale to merely use more humane insecticides without also reducing the quantity of insecticides employed.

## Appendix: Estimating effective insects per hectare using net primary productivity

In the main text I estimated ~88,000 effective insects on a lawn of 0.2 acres. That number was derived from guessing what seemed like a reasonable number of insects per square foot based on what I've seen in real life. This section attempts an alternative estimate based on the net primary productivity of lawn grass.

This study reviews the literature to find an average net primary productivity for grasslands of "5.89 to 12.71 Mg dry matter/ha/year". Since I suspect this paper might be biased to overstate carbon sequestration, and in order to keep my estimate conservative, I'll take a smaller figure: say, 2 Mg. The study says (pp. 809-10) that "Each year, ≈10% of the biomass added to the soil may be humified (Duiker and Lal, 2000; Puget et al., 2005; Schimel et al., 1994)." If we conservatively assume that 10% of all the primary production is humified, that leaves 90% to be consumed immediately: 2 * 0.9 = 1.8 Mg.

How much of this mass goes into biomass of insects, bacteria, etc.? And how much of the energy is expended as heat? Following are some estimates of insect ECIs:

• One page reports: "Tests on two species of edible grasshoppers, Locusrana migratoria and a species of Melanoplus, fed on several kinds of grasses showed combined ECIs in the range of 10-15% and 8-11%, respectively." (Note that the linked page supports entomophagy, which I oppose.)
• This study found ECIs for grasshoppers between 9.5% and 16.5%.
• This study found ECIs between ~2% and ~15%.
• This page says: "For the German cockroach (Blattella germanica), [the ECI] is well above 40. Silkworms, traditionally cultivated in China and neighboring regions, typically have an ECI in the 20-30 span."

Conversion efficiencies for effective insects should be higher than this, since some of what isn't digested by insects will be eaten by bacteria later. On the other hand, the quoted figures are plausibly high-ish ECIs relative to insects in general because insect farmers will tend to use insects with higher ECIs and harvest the insects once they've grown rather than letting them continue to expend energy after they're already at full size. Assuming these considerations roughly cancel, let's take an ECI of ~10%. I assume this ECI is for growing organisms. ECIs for adult organisms should be roughly 0%, since adults tend not to grow further. So all told, the ECI for organisms that eat grass biomass might be, say, the midpoint of 10% and 0%: 5%. 5% of 1800 kg implies 90 kg of heterotroph-organism biomass by dry weight.

This is primary-consumer production per year, i.e., the increase in biomass of primary consumers per year. In temperate climates, this growth only happens during spring-fall months. If we assume for simplicity (if not accuracy) that primary consumers are all univoltine and live from spring through fall, then the standing biomass of primary consumers by the end of the season would equal the annual production: 90 kg per hectare.

Assume that a mass of bacteria/nematodes/etc. equal to the mass of an insect suffers as much as the insect. Then we can convert 90 kg of dry organism biomass into a number of effective insects by dividing by the dry weight of an insect. This page reports that a fruit fly has a mass of 2–3 * 10−7 kg, while an adult housefly has a mass of 2 * 10−5 kg.

Here's another way to estimate housefly mass. An adult housefly is 6-7 mm long. Say the fly has equal volume as a 4 mm cube. Then it would be 43 = 64 mm3 or 0.064 cm3. Assume it's ~half as dense as water and that its dry weight is ~half its wet weight. Then it would weigh (0.064 g)/(2*2) = 0.016 g, or about 2 * 10-2 g, which is exactly the same as the 2 * 10−5 kg figure from the previous paragraph.

Let's take a housefly as our reference insect. Then the number of effective houseflies is (90 kg)/(2 * 10−5 kg per fly) = 4.5 million flies. This is per hectare per year. It's equivalent to 360,000 effective houseflies supported by a 0.2-acre lawn. This is close to my 88,000 estimate, which is surprising given that I didn't fudge with any of my input assumptions in order to make the number come out right.

If you only care about insects, rather than bacteria/nematodes/etc., then the number of effective houseflies would have to be reduced to account for the fact that a lot of grass isn't eaten by insects. If, say, 10% of digestible grass biomass is eaten by insects, that would imply ~36,000 actual insects supported by the grass of an average lawn, which is about the same as the 44,000 estimate I arrived at by guesstimating insects per square foot.

### Estimate using springtails and mites

This article says of springtail bugs: "Ranging from 0.25-10mm in length, there are typically around 10,000 per square metre of soil, rising to as many as 200,000 per square metre in some places." This page says

In sheer numbers, they are reputed to be one of the most abundant of all macroscopic animals, with estimates of 100,000 individuals per square meter of ground,[24] essentially everywhere on Earth where soil and related habitats (moss cushions, fallen wood, grass tufts, ant and termite nests) occur.[25] Only nematodes, crustaceans, and mites are likely to have global populations of similar magnitude [...].

Here are vivid videos showing dense springtails on soil.

A friend of mine (unfortunately!) has a vermiculture bin, and in it, I've seen populations of mites as dense as ~1 per mm2 just on the surface of the bin. That implies ~106 mites per square meter.

Suppose that the decaying grass on your lawn supports 10,000 springtails per m2 = 108 springtails per hectare. Suppose the typical springtail is small -- say 0.5 mm. Above I suggested that a typical housefly is 6-7 mm long. So a housefly is about (6.5/0.5)3 = 2 * 103 times bigger than a springtail. Hence, 108 springtails per hectare have about the same size as ~50,000 houseflies per hectare. That's ~4000 houseflies on a 0.2-acre lawn. And if we count mites and other invertebrate fauna as well, this number might be a few times bigger, putting this estimate in a similar ballpark as the 44,000 estimate of bugs on a typical lawn in the main text.

### Other density estimates

In the main text, I assumed a very conservative 5 bugs per square foot of lawn. This is at least an order of magnitude lower than the densities of invertebrates per square foot of grassland that are reviewed in this 1937 article:

Mr. McAtee in a grassy meadow in March found 1,374 animals in four square feet, or 343 per square foot, but of this number, 933 were one species of ant, Trematoriurn caespitum, and "although there was no ant colony in the plot", yet for comparison with a woodland plot, he subtracts "these strongly contrasting elements", leaving 239 animals for four square feet, or 60 per square foot. This much more nearly approximates the results obtained in the present investigation, which totaled 6,843 animals for the 100 square feet examined, or, to compare with a locality where the climate more nearly approximates that of Washington, those of a previous investigation by the writer in central Illinois [...], where the animal population (counting grasshopper and mealybug egg-clusters as one, rather than each egg as a separate individual) averaged 57.5 per square foot in the fall and early winter, and 82.9 per square foot in the spring.

Mr. Morris [...] records finding 3,586,088 insects per acre, or 82 per square foot in a pasture in England. Dr. Beebe [...] found [...] 65 per square foot of "leaves and moss from an uncleared area in the woods of a New York Zoological Park" [...]. The writer [...] collected 215 ants and 114 other insects and small animals from three square feet of pasture near the beach at Pt. Cangrejos, Porto Rico, or 110 animals per square foot.

## Footnotes

1. If you spray pesticides, the density of bugs on your lawn would be lower, but then you're painfully killing a number of bugs. For this analysis, I assume that the suffering caused by pesticide spraying plus the extra organisms that will feed off of the grass biomass in place of the insects that would have been eating it is equivalent to the suffering of 5 bugs per square foot on unsprayed lawn.  (back)
2. Capturing solar energy that would have helped plants grow reduces insect suffering. The captured electricity will still power some marginally sentient creatures in the form of computers, but the total amount of suffering endured on the part of electronic devices is tiny compared with that of the insects and other small biological creatures that would have eaten the plants that would have existed without the solar panels. Plus, electricity is a small portion of the cost of computing, and most electronic devices will be powered one way or another, although creating more total electricity might ever-so-slightly increase the amount of computation people run. Sadly, most forms of electricity generation -- fossil fuels, nuclear, wind, etc. -- don't (directly) prevent any photosynthesis, except maybe by the small amount of land that non-solar power plants occupy or the tiny amount of shade they produce.  (back)