Summary
While I generally avoid killing healthy insects, I often find injured or dying insects in my house that I try to euthanize. This page describes the two methods I use to kill bugs with as little pain as possible: (1) thorough crushing against rough paper and (2) freezing (which is perhaps less advisable if thorough crushing is feasible). I welcome more research and opinions on euthanasia techniques.
It's not completely clear to me if euthanizing dying bugs is more humane than leaving them to die on their own. For example, I worry that when crushing bugs into little pieces, there's a small chance the animal's tiny brain might remain somewhat intact in one of those pieces? I'd like to find out more about this concern.
Contents
Introduction
It's a difficult question how to handle invertebrates like flies, ants, and beetles in one's house in a way that minimizes total invertebrate suffering (Tomasik "Speculations ..."). I generally err on the side of not killing healthy bugs because my euthanasia methods are probably not pain-free, and I worry about increasing total deaths per unit time by killing bugs prematurely (Tomasik "How ...").
However, it does seem that bug euthanasia is sometimes warranted. For example, if you've accidentally stepped on and half-crushed an insect, you should probably fully crush it immediately rather than leaving it to die slowly. Likewise, I suspect it's better to euthanize slowly dying bugs, such as flies that enter your house in the fall and eventually stumble around from exhaustion. It's an important question where the cutoff is at which euthanasia becomes the better option, and opinions are likely to differ on this point.
This article describes two euthanasia methods that I use. There has actually been research on insect euthanasia (Wikipedia "Insect euthanasia"), but unfortunately, most of those methods are targeted at laboratory researchers who have access to chemicals or other special equipment and expertise. Since almost all bugs that humans kill are killed outside laboratories, there's a need for more research on euthanasia methods that laypeople can use.
Why I worry about incomplete crushing
In my experience, many people assume that quickly swatting a fly or mosquito against an arm or against the wall produces an instantaneous, painless death. While this might sometimes be true, I fear that casually crushed bugs may not be completely killed right away. Evan Gaensbauer wrote regarding his experience swatting bugs in an effort to humanely kill them: "In the past, when I've swatted bugs without checking for signs of life after, I'll come back minutes later to see the bug is still somewhat alive, and is struggling to keep moving" (from a Facebook post, , quoted with permission).
Even if a crushed bug stops moving, are you sure that the relevant neural connections for producing pain have been disconnected or otherwise disabled? Might they still be firing, at least partially? The brain of an insect is plausibly smaller than one of the chunks of mashed-up body parts that result from crushing an insect. Is it possible that the brain remains at least partly intact in one of those insect body-part chunks?
Insects are robust creatures. For example, Choi (2007) explains: "Headless roaches are capable of living for weeks." Part of the reason why is that "The hardy vermin breathe through spiracles, or little holes in each body segment. Plus, the roach brain does not control this breathing and blood does not carry oxygen throughout the body. Rather, the spiracles pipe air directly to tissues through a set of tubes called tracheae." Moreover, insect nervous systems are somewhat decentralized (Choi 2007):
Insects have clumps of ganglia—nerve tissue agglomerations—distributed within each body segment capable of performing the basic nervous functions responsible for reflexes, "so without the brain, the body can still function in terms of very simple reactions," Tipping says. "They could stand, react to touch and move."
In discussing how to fight the giant ants in the movie Them!, LaBarbera (2013) explains:
Insects have a much more distributed nervous system than vertebrates, so the head is a pretty poor target. So is the body. Because of their highly efficient respiratory system [...], circulatory demands are much lower in insects than in vertebrates; insects can get away with a fairly low-pressure circulatory system. A hole in the exoskeleton, even a 30-caliber hole, just isn't going to bleed much, and the hole will be quickly sealed because insect blood has excellent clotting characteristics.
starsplusplus (2014, "How do ...") says regarding crickets: "I have also heard the suggestion that you can crush their heads with feeding tongs or tweezers as a humane way of killing them. However, it's not very practical if you have hundreds of them. There is also some debate as to how humane this method is, because the insects remain alive for a while after having their heads crushed."
Following rainstorms, earthworms often inundate sidewalks near soil-rich locations. These worms may be crushed by inattentive pedestrians. In 2009, I asked entomologist Jeffrey Lockwood for his informal guesses about the fate of worms who are partly crushed by people's feet. Lockwood replied: "My sense is that it takes a rather long time for a partially crushed worm to die, as its physiology and anatomy are such that death would not follow nearly as quickly as it would for a mammal with a more complex and concentrated set of vital organs" (qtd. in Tomasik "Worms ...").
So if insects are to be crushed, I think they ought to be completely crushed into tiny pieces. I would be curious for a neuroscientifically literate entomologist to advise about how valid the above concerns are and whether complete crushing can fully destroy or at least inactivate the relevant nervous connectivity. Also, how long does it take after an insect is thoroughly crushed for neurons to stop firing?
Does crushing a bug's head burst open its neurons or otherwise destroy them? Or is the tissue of the insect more like a bean bag, where the material inside deforms without being destroyed, similar to a squashed cartoon character (TVTropes "Squashed Flat")? Even if the neurons themselves aren't destroyed, hopefully the squashing process disconnects a lot of synapses by moving neurons around? Without knowing how the physiology of squishing works, my guess would be that it's very likely that sufficiently hard squishing does significantly destroy nervous connectivity. But even if the probability that it fails to do so is only like 1%, given how much pain the bug might be in if the brain isn't immediately destroyed, I feel like this concern warrants further investigation.
Method 1: Immediate, thorough crushing
When I find an injured bug requiring euthanasia, I gently pick it up and bring it to the part of my house where I keep a flat piece of wood and sheets of rough scrap paper or paperboard (such as the rough side of a cereal box). I lay the bug in the middle of the paper, bang the flat wood on it as hard as possible, and then continue a succession of banging and scraping motions. I scrape the bug out over the paper in order to fully flatten it, using the rough surface of the paper to trap small bug particles. (Smooth paper doesn't work as well, because the bug's body is more liable to just slide around without coming apart.) I continue scraping and banging on whatever parts of the bug's body seem incompletely disintegrated.
This process is illustrated in the following video: "Sped Up Footage of a Dying Fly". Make sure to wash your hands after this procedure.
If I don't have my wood block nearby, I can also crush small bugs (like fruit flies or aphids) with my fingernail against a piece of paper or paperboard. Then I use my fingernail to scrape up the crushed body and crush it again until all parts are flattened.
If you're outside on a road or sidewalk, you can crush bugs by sliding your shoe over them back and forth to flatten them out on the pavement. In my experience this doesn't crush the bugs as well as using paper, because the pavement is more rough and uneven than paper is, so the bug chunks left over tend to be bigger. Plus, if the bottom of your shoe is not completely flat, some parts of the bug may remain uncrushed in your shoe's grooves. Given these concerns, I typically only do crushing on pavement for large invertebrates, like injured earthworms or grasshoppers who have collided with cars. With large invertebrates, even if pea-sized chunks of the body remain uncrushed in the pavement or a shoe groove, the chunks are still only a small fraction of the total body size, so hopefully most high-level nervous-system connectivity has been destroyed? Because crushing involves tissue damage over the whole body, the process may be intensely painful for a few seconds (...hopefully not longer, but I don't know for sure), which makes me question whether it's actually more humane than leaving the bug to die. If you do leave a bug to die, it's best to move it off of the sidewalk so that other people won't continue to step on it.
You could potentially carry around a small plastic container in your backpack or purse that you could use to collect any injured bugs you find on the road or sidewalk, bringing them back home for crushing or freezing with proper equipment (idea inspired by Benjy Forstadt, , cited with permission). Of course, if you won't return home for a while and the bug seems to be in pain, crushing it imperfectly on the spot may be better. You could alternatively carry around paperboard and a piece of wood in order to crush injured bugs that you see outdoors, though doing this would get your hands dirty, and you wouldn't have a sink nearby.
I think crushing is probably the best method of euthanasia for bugs with soft, easily destroyed bodies—including flies, moths, and carpet beetles. However, I find that it doesn't work as well for other bugs. For example, ants and ladybird beetles have hard exoskeletons, making it difficult to fully crush their bodies. Meanwhile, caterpillars and fly larvae are rubbery and so can also be hard to thoroughly crush. For these insects, freezing (see next section) might be a better option. On the other hand, since freezing takes a while to work, if you have a bug that's acutely injured and writhing in pain, squishing is probably warranted in order to kill it quickly.
If you have a large number of invertebrates and are too lazy to carefully crush them one by one, then freezing (discussed next) might be a reasonable alternative. For example, if you find a mass of fly larvae writhing in a food-scrap container, freezing the container for a while to prevent the larva population from growing further may be a good idea. (You can also pre-freeze food scraps to ensure that any bug eggs they may contain don't hatch.)
While I conjecture that thorough crushing of a bug is perhaps somewhat more humane than freezing it, if you don't want to take the effort to completely crush the bug, then it's plausible that freezing is the better option, because freezing ensures that the bug will die, while a poorly crushed bug might suffer for a very long time without actually dying.
In principle, you could even use both methods: thoroughly crush a bug against paperboard and then put the paperboard in the freezer so that in case any bug parts still have active neurons firing, those neurons will be put to rest. Of course, doing this takes more effort than just using one killing method, and if that effort is annoying, you might be tempted to stop bothering with humane killing altogether. It's important not to let the perfect be the enemy of the good.
Method 2: Freezing (probably less advisable)
I oppose insect farming because it causes suffering to large numbers of animals (Tomasik "Why I Don't ..."). However, it can still be instructive to learn about how insect farms kill their victims. Some (though unfortunately not all) insect farms freeze insects to slaughter them. In King (2014), Robert Nathan Allen explains regarding farmed insects: "when they're culled we lower the temperature so that there's no violent death or change in state (because insects are exothermic their metabolism slows until they go into a coma-like sleep without any pain)."
Without more study of this issue, it's unclear to me if freezing is indeed humane. As I mention below, entomologists are uncertain on the matter. However, it does seem plausible that freezing is qualitatively different for an ectotherm than it would be for us, especially an ectotherm that cools quickly due to a small mass-to-surface-area ratio. An endotherm put in a freezer will use its energy reserves to actively fight the cold temperature; it will remain conscious and distressed for a while. In contrast, it may be that a small ectotherm put in a freezer "shuts down" after a few seconds or minutes, because it's too cold for bodily functions (including neuronal firing) to occur.
starsplusplus (2014, "How do ...") says about disposing of excess crickets: "The most humane and efficient way of disposing of them, especially if you have large numbers, is to tip them into a bag, seal it closed and place the bag in the freezer for 24 hours. (You can double-bag it if you're worried about contaminating your food.)" starsplusplus (2014, "How do ...") argues that "Insects are ectothermic, which means that in cold temperatures their metabolism just slows down until they die. The insects go into a cold-induced coma from which they do not recover."
I unfortunately have a lot of experience with freezing flies and other bugs around my house in order to euthanize them. Usually I drop a bug into a plastic container that stays in the freezer. Since this container is cold, the bug also gets cold quite quickly. When I put a fly into this container and then reopen the freezer to check on it a few seconds later, I find that the fly stops moving within ~10 to ~20 seconds. (I only reopen the freezer door on rare occasions for the purpose of measuring how long it takes for the bug's activity to stop. Most of the time you should presumably keep the freezer door closed so that the bug gets cold as quickly as possible.) One hopes that lack of movement also indicates lack of neuronal activity in general, though it's hard to know if that's the case until scientists look into the matter more thoroughly. Of course, "not moving" doesn't mean "dead"; a bug might recover if unfrozen. So it's best to keep the bugs in the freezer for a very long time to ensure that they fully die.
While a fly put into an already cold freezer container typically stops moving within several seconds, if a fly is put into the freezer in a plastic bag or cup that wasn't yet in the freezer (and therefore starts out at room temperature), the fly may take several minutes to stop moving. Maybe this is because when the fly is put in a container that's already cold, the container itself can make the fly cold quickly, while if the fly is in a room-temperature container, the removal of the fly's heat has to be done mainly through the freezer's air, and air is a poor conductor of heat?
During the spring in my house, there are unfortunately lots of dying housefly-type flies. These flies overwinter in the warm house and come out of hiding as the temperature increases in the late winter and early spring. I sometimes kill these flies so that they can avoid a grueling days-long process of dying on their own and so that they're less likely to be accidentally stepped on. On , I caught one of these flies in a plastic "slider" bag. The fly was upside down and wiggling its legs constantly. I put the fly in the freezer and waited about 20 seconds. Then I briefly opened the freezer door and saw the fly's legs still moving pretty quickly. I closed the door and waited about 20 more seconds. Upon reopening, I saw the fly's legs moving but more slowly. I closed the door for about 30 seconds and upon reopening saw the fly completely still. (I didn't have a stopwatch handy, so these are just my approximate guesses of the durations.) Given that it took more than a minute for the fly's movement to stop, I worry that this process might be pretty painful. Plausibly I should have crushed the fly instead of or prior to freezing it, though it can be difficult to crush flies when they're moving around too much. I'm unsure if freezing is a better death than letting these flies die on their own of other causes. (Basically all of these flies in my house do end up dying within a few days of reanimating. I'm not sure what they die of—maybe dehydration?) These flies come indoors in the fall as the weather gets cold, so presumably they are averse to cold temperatures. If I open a window temporarily in the winter, if there are housefly-type flies hiding in parts of that window, they tend to huddle up in a corner away from the cold wind, which again suggests they plausibly dislike cold temperatures...
Turner et al. (2016): "we investigated the cellular and molecular bases of cold nociception in Drosophila larvae. Acute noxious cold provoked a set of unique behaviors with a full-body contraction (CT) as the primary response. [...] Our findings reveal that Drosophila uses a distinct set of cells, channels, and aversive behaviors to respond to extreme cold."
Some researchers do euthanize insects by freezing. Groening et al. (2017), after experimenting on bees, killed them by freezing: "At the end of each replicate, bees were sacrificed by freezing".
The "BIAZA Recommendations for Ethical Euthanasia of Invertebrates (Version1.1-Apr2013)"a says of freezing (p. 3) that "research has suggested that this is probably one of the least ethical options (Bower et al, 1999; Pizzi et al, 2002; Pizzi 2012)." Freezing (p. 9) "Does not provide muscle relaxation or analgesia effects. Considered to be inhumane without prior anaesthesia." However, this statement is directed at scientists who have access to fancier euthanasia equipment. The BIAZA paper also says (p. 8):
Ideally, surplus invertebrates or invertebrates requiring euthanasia should be taken to a veterinary practice. However, this may not be practical or possible. Most members of the public do not have access to any chemical methods therefore physical crushing or freezing is still being advised by some institutions. Freezing is increasingly regarded to be inhumane without prior anaesthesia (Pizzi, 2012). However, if there is no alternative and euthanasia of an invertebrate MUST be carried out at home it is best to refrigerate first for a minimum of four hours then place the individual in the coldest freezer possible for at least two hours (Bushell, personal communication).
I freeze insects by capturing them in a Ziploc bag and then putting that in my freezer. Based on the above BIAZA quote, I probably should refrigerate them first, but sadly, I usually don't.... Besides laziness, one reason for this is that I put a lot of bugs in just a few bags, and I'm nervous about handling insects more than necessary by transferring them from a "fridge bag" to a "freezer bag", since handling an insect poses the risk of injuring it. I usually just put them in the freezer bag directly. Once a bag is in the freezer, I don't want to take it out again for more than a few seconds in case the bugs already in it will unfreeze and wake up. I suppose you could have a "fridge cup" that stores an insect in the fridge, and then after a few hours you could tip this cup upside down into the freezer bag or freezer cup; this would avoid the need to pick up the insect with your fingers, preventing the risk of crushing it.
If an insect you're trying to capture in a Ziploc bag can crawl, you can try to get it to crawl into the bag, or coax it to crawl onto a shred of paper that you can then deposit into the bag. If the insect is small and immobilized, you can try to blow it into the bag. Picking up a bug with your fingers is risky because you might crush parts of the bug while doing so. Before capturing insects, I try to blow some air in the bag so that the bag will puff outwards. That way, the insect won't get crushed between the two halves of the bag. If the insects are already in a container—e.g., fruit-fly larvae growing in a container of food scraps—you can refrigerate and then freeze (or just freeze, if you're lazy) the whole container directly.
[Update from 2024: The suggestions in the above two paragraphs are old and overly complicated. My current method is to use sealable plastic containers (such as an old plastic jar for dry roasted peanuts) that I put in the freezer. I also have a collection of old magazines from which I can tear off small pieces of paper that are a few centimeters wide and long. If I see an injured bug, I tear off two small pieces of paper and use them to scoop the bug from the floor onto one of those pieces of paper. I carry the bug to the freezer and drop the bug into the container, or I drop the entire paper piece in if the bug is stuck to it. This method doesn't require any blowing (which can get dust into your lungs), doesn't risk crushing the bug with fingers, and doesn't get your hands dirty. If you're less lazy, it would be better to use this method to deposit a bug into a fridge container that you later dump into a freezer container.]
I don't know how long it takes insects to die in a freezer, especially a home freezer that's not necessarily maximally cold. As a precaution, I leave insects in the freezer for at least months, because I see no strong reason to take them out earlier. If you drop new insects into the same freezer bag or freezer cup as old ones, then they don't take up much space.
Invertebrates can often survive frosts or even a few days of snow in the fall/winterb (although perhaps with the help of burrowing or other escape measures), which makes me question whether freezing for mere hours or days is sufficient. In general, some insects are extremely good at surviving cold winters (Wikipedia "Insect winter ecology"), which I take to imply that you should keep insects in the freezer for a very long time, unless you know that a particular species dies quickly from freezing.
Texas A&M AgriLife Extension Service (n.d.): "freezing is a preferred method of killing insect specimens. Most specimens will die over night but some cold resistant insects may require a week or more to die." starsplusplus (2014, "How do ...") suggests that if you freeze crickets, "After 24 hours all the insects will be dead". On the discussion starsplusplus (2014, "How long ..."), user "WYSIWYG" says regarding crickets: "How long it takes to die depends on the freezer temperature; based on personal experience I can say that they die in ~10min @ -20⁰C." The same comment also mentions a paper finding that "Drosophila will die in less than 2 hours at -5⁰C upon transferring them to the cold temperature directly (cold shock). However, if the larvae are 'hardened' by keeping at +5⁰C before cold shock, their survival chance increased — the temperature required for killing them in 2h (Lowest Lethal Temperature) reduced." These data points are useful, but I would be wary of taking them too much at face value because there's probably significant variation depending on species and circumstances. This is why I favor keeping insects in the freezer as long as possible (up to a few months), unless there's a strong reason to remove them sooner.
In order to keep bugs in the freezer for a long time while also adding new ones regularly, you'll need at least two separate containers stored in the freezer, which we can call Container 1 and Container 2. These could be old yogurt containers, small Tupperware, or something similar. First put all bugs into Container 1 until it fills up. Then start adding bugs to Container 2, but keep Container 1 in the freezer for a few months. Once even the most recent additions to Container 1 have been sitting in the freezer for a few months, empty Container 1. Keep filling Container 2 until it's full. Then switch back to Container 1, but keep Container 2 in the freezer for a few months before emptying it. And so on. When you empty the frozen bugs out of a freezer container, I recommend putting them into a sealed plastic slider bag or some other sealed container before throwing them in the trash. Sealing makes it less likely that invertebrate or vertebrate animals will eat the dead bugs in the trash can. [Update from 2024: I use four different sealable plastic containers in the freezer at once. I fill up the first, then the second, then the third, and then the fourth. By this point, the first has been sitting full for a few weeks or more, so I throw it sealed in the trash and get a new container. The reason my containers fill up somewhat quickly is that I also use them to dispose of small food scraps, such as banana peels or bad spots on cucumbers, in a way that keeps those food scraps out of the reach of fruit flies. If I threw out food scraps into a container outside the freezer, I'd have to open it and re-seal it each time, which is somewhat more work, and the container could get my hands dirty/sticky.]
The possibility of cold hardening is troubling, because I imagine it might significantly increase the length of time before an insect dies in the freezer? Or are freezers sufficiently cold that cold hardening is irrelevant except for the most cold-tolerant insects? Does cooling insects in the fridge prior to freezing them increase cold hardening?
Even if cold hardening isn't an issue with pre-refrigeration before freezing, I also wonder whether pre-refrigeration might be less humane just because the insects remain alive for vastly longer, compared against freezing directly? In my experience, when flies wander into my fridge, they usually stop moving, but they can actually still move if you poke them or frighten them. It's only after some period of hours or days (I'm not sure how long exactly) that flies who have wandered into the fridge actually seem to die (from cold? from dehydration?). In contrast, flies put into the freezer become permanently immobile in less than a minute. How does the possibly intense pain of being put directly into the freezer compare with possible stress during the much longer period of cooling in the fridge? Maybe cooling in the fridge is painless, given that insects in nature experience significant temperature fluctuations on a daily basis? Anyway, the experts seem to advise pre-refrigeration before freezing, and I'm inclined to assume they know what they're talking about, though I'm curious whether they've considered these questions.
In 2024, I asked an entomologist with interests in insect welfare and physiology about pre-refrigeration. The expert replied: "I think refrigerating is probably better prior to freezing, in that it gives the animal time to physiologically adjust to the cooler temperatures - and we know that at least some insects may go through regular freeze-thaw cycles when it cools at night versus gets warm in the morning. This physiological adjustment period may allow them to make the process of cooling less painful/stressful by modulating nociceptive responses in the nervous system. While this is likely to cold-harden the bug (e.g., they may survive a few more seconds in the freezer than they would otherwise), I think it may still be overall better for their experience. But I have a lot of uncertainty about everything I've just said" (, quoted with permission).
Freezing is not a humane method of euthanasia in larger animals, including ectothermic ones. For example, Barten (1994/2014) explains: "Freezing has been used as a humane method to kill small reptiles under one pound in weight. Although low temperatures do result in a state of torpor, the formation of ice crystals in the tissue is quite painful. Freezing should only be done to anesthetized animals." Likewise, there's debate on the humaneness of freezing in invertebrates. For these reasons, I prefer thorough crushing of bugs when possible, and I'm not even sure if freezing is better than simply leaving a bug to die in some other way, such as from dehydration or starvation.
As is the case for reptiles, ice crystals can form in freezing insects. Golding et al. (2023) report that at -7°C, "ice crystallization occurs within the snow fly's hemolymph and rapidly spreads throughout the body, resulting in death. However, we discovered that snow flies frequently survive freezing by rapidly amputating legs before ice crystallization can spread to their vital organs." In other words, at least some cold-adapted insects remain conscious as their tissues begin to form ice crystals.
I would be nervous about freezing bugs within water, in case the formation of ice around them would crush them? In other words, I wonder if you should only freeze bugs when they're dry?
If you use bait traps to reduce the populations of bugs like fruit flies in your kitchen, it's better to freeze the caught bugs (ideally dry, not in liquid) rather than, say, drowning them. Of course, preventing fruit flies and other pests from establishing a population in the first place should be your main priority. For example, you can put food waste in sealed plastic slider bags before throwing it out to avoid letting fruit flies breed in your trash cans.
In contrast to freezing, heat is probably a particularly BAD way to kill bugs. Many studies find that bugs react aversively to excessive heat and can learn to avoid it. Texas A&M AgriLife Extension Service (n.d.): "heated specimens become overactive and will be more likely to injure themselves in the process. It is also cruel!" For killing bugs en masse, freezing is probably much better than heating.
Faster freezing with a metal container
A reader wrote to me regarding the freezing methods discussed above (, quoted with permission):
You mention correctly that air is a poor heat conductor. However, plastic is also a relatively poor heat conductor. Metals, however, are great heat conductors!
The person suggested dropping bugs into an aluminum jar in the freezer. The jar should be kept in the freezer all the time so that it stays cold. If the jar started out at room temperature, the bug wouldn't cool down nearly as quickly.
Eventually an aluminum jar for freezing bugs might accumulate a pile of bugs on the bottom, which would reduce thermal conductivity. So you could get a small aluminum cup into which you drop new bugs, and then once they're initially frozen you could later dump them into a larger container for keeping in the freezer for a long time until you eventually throw them out. This setup also means you can throw out bug containers without throwing out aluminum (since the initial aluminum cup is reused). I generate lots of spare plastic containers from eating peanuts. If you generate waste plastic containers from food anyway, you can use those to store bugs in the freezer for a few months and then dispose of them without having to buy containers specifically for this purpose.
As I mentioned above, I throw out small food scraps into these jars in addition to bugs as a convenient way to keep food scraps out of the trash can, where they might breed fruit flies. If you drop bugs directly onto an icy food piece, how good of a heat conductor is that? The reader said: "Ice is 1 [order of magnitude] better than plastics, but 2 [orders of magnitude] worse than metal. Therefore I'd still recommend metal, if possible" (, quoted with permission).
It's not completely clear to me that faster freezing on metal is better than slower air freezing. Maybe air freezing would gradually quiet the nervous system, in a similar way as pre-refrigeration might? And if air freezing is less painful per second, that might compensate for a larger number of seconds required to freeze. As an analogy, I would probably rather die from heat stroke over the course of an hour in a moderately overheated room than die within a few seconds by sinking into a 1000°C liquid, because heat stroke can sometimes induce unconsciousness before too much bodily degradation occurs and because the pain of heat stroke would be vastly less intense per second. In any case, hopefully freezing metal isn't as painful as extremely hot liquid, and if a bug would die many times faster on metal than on plastic, that does prima facie seem like the better choice without knowing more about exactly how painful freezing metal vs freezing air are.
Shredding?
I'm interested in the possibility of euthanizing insects using some kind of fine shredder. Some farmed insects are killed by shredding.
I looked on Amazon at food shredders, trying to find one that had blades as close to the bottom as possible so that it would be more likely to shred insects, which aren't very tall. Cuisinart SG-10 Electric Spice-and-Nut Grinder seemed to have relatively low blades, so I tried ordering it. When it arrived, I saw that the blades were still probably too high to do a great job shredding, but I tried it out on some already long-dead insects that were lying around (ladybird beetles, houseflies, and a wasp). Even though the blades were high, these bugs were cut up into several pieces. However, because the dead bugs were quite dry, I'm not sure how much of this shredding was due to their inherent brittleness combined with the motion of the whirring grinder. Probably wet insects would have been harder to cut up. Also, the bug pieces weren't quite as small as those I create when crushing using wood and paper (as described in "Method 1" above). So for now I'll stick to wood and paper, but the shredding idea deserves more exploration.
I also tried adding a bit of water to the nut grinder so that the insects could float closer to the blades. I'm not sure if this helped (maybe a bit?), but the resulting chunks were still sometimes bigger than I was comfortable with.
If shredding can be made to work, it has advantages over crushing by hand, including being easier, more sanitary, less messy, etc.
Wanted: A humane bug-killing device
In the long run, someone should work on building a consumer device that can humanely kill bugs. The problem doesn't seem that hard, especially if it's possible to shred bugs into really small pieces. Imagine a future where people can buy on Amazon for $50 a simple box-shaped device that you can drop bugs into in order to humanely kill them.
Here's an extremely rough cost-effectiveness calculation for an effort to build a humane bug-killing device and sell it on a large scale. Suppose that one person who has an opportunity cost of $200,000/year spends 5 years developing a humane bug-killing device and building a startup company around the product or trying to pitch it to larger manufacturers. Such an effort would almost certainly fail, but suppose that it has a probability P of succeeding so well that the humane bug-killer becomes a common household device throughout the developed world.
In particular, suppose that if the device succeeds wildly, 1 billion people would use it, each giving, say, 50 bugs per year a much more humane death, for the next, say, 50 years. The expected number of painful bug deaths averted per dollar would then be
P * (1 billion people) * (50 bug deaths per person per year) * (50 years) / (5 * $200,000) = P * (2.5 million) bug deaths per dollar.
What is P? I don't really know, and someone with more expertise in the success rates of consumer-product innovations could comment here. It seems like the prior probability for any given new product to become so common that most Western households have it is quite low, because most Western households only have so many products, while the number of products people develop is vast. I would guess that P should be no greater than, say, 10-4, and maybe 10-5 is a reasonable or even optimistic parameter estimate. Using P = 10-5, the cost-effectiveness becomes 25 expected painful bug deaths prevented per dollar.
What is this in terms of invertebrate-years of suffering? In Tomasik ("Cost-Effectiveness ...") I suggest that, very roughly, "An insect-year of suffering is equivalent to the pain of dying for on the order of ~10 adult insects". So 25 painful bug deaths prevented would be 2.5 invertebrate-years of suffering prevented. On the other hand, many of the bugs that people kill in their homes, such as houseflies, ants, beetles, etc. are bigger and more cognitively sophisticated than small bugs like mites and springtails that dominate in counts of invertebrate-years of suffering in natural habitats. If we give a typical bug that humans kill in their homes, say, 10 times more moral weight per individual than a typical invertebrate in the wild, then we could bump the cost-effectiveness up to 25 invertebrate-years of suffering prevented per dollar. Since these numbers are so incredibly crude and made-up, in order to avoid false precision, we can represent this as just ~102(??) invertebrate-years per dollar.
Caveats on the calculation
In the above calculation, I didn't count any costs that a humane-bug-killer company would face after initial startup because private investment could probably cover it. I'm also not counting further time investment by the founder if the company is successful, because the company is so unlikely to be successful in a big way that this time cost is negligible in the expected-value calculation. Also, if the company succeeds, it would yield profits, which would offset these costs. Once again, this kind of big success is so unlikely that it doesn't factor significantly into the calculation.
I'm ignoring higher-probability scenarios where the product is less wildly successful because intuitively they seem less significant. For example, a 10-5 probability of reaching 1 billion people is an expected 104 people, while, say, a 10-2 chance of reaching 10,000 people is only an expected 102 people.
My calculation ignores possible memetic benefits of spreading a humane-bug-killing device for people's overall concern about insect welfare.
Perhaps technology for humane bug-killing could have much larger impact applied to the entomophagy industry than marketed to individual households.
Finally, it's plausible that information on the possible success of this kind of project could be gained with much less than 5 years of a skilled device-developer's time. The cost-effectiveness of further basic exploration of this idea may be higher than 102 invertebrate-years per dollar.
Footnotes
- This document is sadly not available online. I got a copy by contacting BIAZA using the email address found on its website. (back)
- For example, in Tomasik ("Invertebrates ..."), I show a number of active invertebrates outdoors on November 15, even though "the temperature had already been below freezing a few times, including once when it snowed several weeks earlier" (0m30s). (back)