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  • There are between 4.2 million and 7.8 million pet snakes in the world.
  • 85 million to 2.1 billion vertebrates are killed for pet snake food every year. I think that the true value is more likely to be on the lower end of this range. Most of the vertebrates seem to be farmed mice.
  • Feeder mice are killed when they are anywhere between 48 hours and more than 9 months old. Most seem to be slaughtered when they are 3–4 weeks old.
  • Farming of feeder animals seems to involve considerable suffering because they are often living in cramped and possibly unsanitary conditions, which don’t have shelters to hide in, lack daylight and activities.
  • I haven’t figured out what possible interventions in this space could be particularly promising. It’s possible that the problem is not very tractable.

In this article, I first estimate the number of animals raised for pet snake food in the world. Then I discuss some welfare concerns of these feeder rodents by comparing the conditions in which they are raised to the ones recommended for pet mice. Finally, I brainstorm about possible interventions.


This article is a part of a series of articles by Rethink Priorities about animals farmed for various purposes. We are also planning to write about fish farmed for fish stock enhancements, and considering writing about the mortality of farmed food animals. Finally, we will create a list of estimates of numbers of animals kept in captivity for various purposes. After that, we may create a similar list of estimates of numbers of wild animals humans affect in various ways. The main goal of the series is to uncover sources of animal suffering that other organizations could tackle with cost-effective interventions.

After writing this exploratory article about feeder rodents, I remain largely uncertain about the scale and especially the tractability of this problem. I look forward to reading opinions about it in the comments.

Estimating how many animals are killed for snake food per year

In this section, I'll produce two different 90% subjective confidence intervals of numbers of vertebrates killed for pet snake food and combine them into one:

  • I first estimate that there are 4.2–7.8M snakes bred to be pets in the world and that on average they are fed 0.6–1.8 vertebrates per week. I then use these numbers to estimate that 85M–320M rodents are killed for pet snake food per year.
  • I then look at some figures of frozen mice sold in the U.K. from the Federation of British Herpetologists and use them to estimate that 540M–2.1B rodents are killed for pet snake food per year.
  • Finally, I make some hypothesis about why the two estimates differ so much, and combine the two confidence intervals into one by taking the lower bound from the first estimate and the upper bound from the second estimate.

For brevity, in the article I use K for a thousand, M for a million, and B or a billion. Many details of the estimations can be seen in the Guesstimate model. Readers who are uninterested in the details of the calculation can skip this section.

Number of pet snakes

I haven’t found any estimates of the number of pet snakes in the world, but I have found some estimates for various countries:

  • According to the UK’s Pet Food Manufacturers’ Association’s (PFMA) surveys, in the UK there were
  • According to the American Veterinary Medical Association (2012), there are 1.15M snakes in the U.S., owned by 550K households. According to the same source, in 2007 there were 586K pet snakes in the U.S. Publicly accessible information did not explain how these numbers were estimated.
  • ENDCAP (2012): “insiders estimate approximately 250K boids and pythons and 100K venomous snakes are kept in private households in Germany.”
  • This Pultizer Center article claims that “it is estimated that up to one one million people own exotic pets in China. These pets are defined as non-traditional ones, such as snakes, monkeys, crocodiles, spiders, and tropical birds that are sourced from threatened ecosystems across the world.” It also claims that owning exotic pets is quickly becoming more popular in China.
  • A survey by Animal Medicines Australia found that there are ~415,000 reptile pets in Australia (sample size was 2K respondents).
  • An Irish Examiner article claims that “Ireland is home to 100K reptile pets, including deadly snakes and crocodiles.”
  • This quora thread suggests that pet snakes may be rare in India.
  • A New York Times article claims that "Exotic reptiles and amphibians began surging in popularity in the early 1990s, not only in the United States but also in Europe and Japan.” I haven’t found any other mentions of pet snakes in Japan.
  • Various articles mention that in Indonesia snakes are sometimes kept as pets, as well as used for food, performance, and massage.

Using this information and some other information, I estimated that there are between 3.8M and 6.9M pet snakes in households around the world. See my guesstimate model for the estimation. The model includes guessing the number of snakes per 1000 people in countries for which I couldn’t find statistics.

Some snakes that are bred to be pets are in pet stores and snake breeding facilities. For example, in Blackpool, UK (population 140K) there are at least two shops that sell snakes. I visited one of them and counted 126 snakes on its shelves, which is almost 1 per thousand people. This shows that the number of snakes in pet shops is significant. I guess that the percentage of such snakes that are yet to be purchased is somewhere between 3 and 20%. With this taken into account, I estimate that there are 4.2–7.8M snakes that are bred to be pets.

Average number of animals fed to snakes

How often snakes are fed depends on species. It seems that for all species, young snakes should be fed smaller mice more often. For example, according to a ReptiFiles.com article, Corn Snakes have to be fed 1–3 smaller mice every 7–10 days until they are 18 months old (number and size of feeder mice depend on age). Ball Pythons should be fed every 5–7 days when they are young. However, snakes spend most of their time being adults. This page lists the five most popular pet snake species. Here is how often each of them should be fed as adults:

It’s possible that some owners choose to feed adult snakes multiple smaller mice rather than one big mouse/rat. Or that some people feed them more often than guides suggest. Manual of Exotic Pet Practice mentions that “snakes are often overfed in captivity.” This informal poll shows that many owners feed one rodent per week and quite many feed more. I also asked how often snakes should be fed at one reptile store and I was told that almost all of their snakes are fed one mice of appropriate size per week, while few bigger snakes are fed more often. But I imagine that reptile stores mostly sell young snakes which need to be fed more often, hence this may not be a good indicator of how often all captive snakes are fed.

A person with knowledge on the subject also mentioned that some snake species (e.g. ball pythons) sometimes go on "hunger strikes". However, they also said that most owners will continue to feed the non-feeding snakes once a month and the uneaten rodents are often thrown away (although sometimes they are fed to other snakes). This probably shouldn't impact the numbers much.

Note that mice are not the only animals snakes eat. A PetHelpful article claims that there are pet snakes that eat chicks, fish, insects, eggs, and reptiles. VCA Animal Hospitals claims that the most popular pet snakes usually eat prey such as mice, rats, gerbils, and hamsters. Larger pet snakes will also eat whole rabbits. At the extreme end, this itv news report about possibly the longest pet snake in the UK claims that it eats 3 rabbits per week.[1] Based on all this information, I guess that on average pet snakes eat 0.3–1 vertebrates per week, which is 15.6 to 57 vertebrates per year.

Number of animals killed for snake food each year (first calculation)

To calculate it, I multiply the number of snakes in the world by the number of animals they eat per year. I also guess that 3%–20% of snakes kept to be pets are in pet stores and breeding facilities. After taking that into account, I get a 90% subjective confidence interval that there are 85M–320M animals fed to pet snakes per year.

An alternative estimate that uses frozen rodents sales

I found some sources that directly say how many frozen rodents are sold. They are much higher than I expected:

  • This Independent article claims that 180M rats and mice were raised in the U.S. in 1999 and that 93% of them were sold as reptile food (other 2% were sold as pets, the rest were used in research). It also claims that there is still a significant shortage of rodents. These figures are especially surprising because it seems that snakes are becoming more popular in the U.S.,[2] but it could be that they were briefly very popular around 1999. The article also mentions that there are 20M reptile owners in the U.S., but I’m not sure I trust this claim. This HSUS document claims that “more than 3.9 million households in the United States contained one or more pet reptiles or amphibians in 2000”. Assuming an average household size of 2.6, that is 10M owners, not 20M. And some of the 10M only kept amphibians.
  • Federation of British Herpetologists' (FBH) website claims that over 1M frozen mice are sold each week for snake food in the UK and that additional ~3.5 tons of frozen rodents are imported from outside the EU each month. It’s based on a 2008 survey by REPTA which I was unable to find. FBH also used this and other sales of specialists reptile food data to determine that there are “over 1.2 million households were home to over seven million pet reptiles” in the UK. Even though FBHs estimates are cited by Telegraph (a respected news source in the UK), I’m not sure I trust this conclusion because PFMA’s surveys consistently estimate that the number of reptile pets in the UK is less than a million.[3] It’s possible that FBH themselves don’t know why so many frozen rodents are being sold or that they are (intentionally or not) inflating the figures.
  • 2012 FBH’s brochure claims that an estimated 2M frozen mice are sold for snake food in the UK each week and also cites REPTA as the source. That is 104M per year for the UK alone. Note that these numbers are only for sold frozen mice, but some people feed their snakes rats, day-old chicks, or other animals.

Even if FBH’s estimate of the number of pet reptiles is incorrect, it’s possible that the sales of reptile food data that was used to produce the estimates is correct. However, in that case, there is an inconsistency between PFMA’s estimate that there are 200K–400K pet snakes in the UK and FBHs claim that 1M–2M frozen mice sold are sold each week because that would be 3–8.5 frozen mice per snake per week - much more than average snake eats. Similarly, if we assume that in 1999 there were as many snakes in the U.S. as in 2007 (586K) and that figures in the Independent article are correct, that would mean that in the U.S. there were 5.5 rodents raised per snake. There are multiple ways to explain these inconsistencies:

  • Contrary to what FBH claims, many frozen mice are used for things other than snake food. According to a Pet Age article, ”the feeder rodent industry may be the lifeblood for snake breeders and snake keepers, but it also serves animal collections at zoos and museums and some ravenous raptors at wildlife rehabilitation facilities.” The article also claims that bald eagles can eat 15 frozen mice in a sitting and that crows and swallow-tailed kites eat small mice. What is more, some lizards, frogs, hedgehogs, and other pets may also eat rodents.
  • There are more snakes in the U.K. and in the U.S. than surveys suggest because surveys don’t capture a few owners who own many snakes. The combined sample size of PFMA’s surveys is more than 24K. Even though it is big, it could be insufficient. If few owners own many snakes, PFMA’s surveys might have failed to catch any such respondents and consequently underestimated the number. According to the PFMA’s surveys, snake-owning households on average own 1.8 snakes. Figure 5 in Clark (2012) shows that out of 656 respondents who owned a snake, 367 owned 6 six or more of them. Survey did not have a representative sample because it was “distributed over the reptile keeper’s networks on the internet,” but it still indicates that there are people who own many snakes.
  • Some sold frozen mice end up not being fed to any animal. In the U.S., human food waste is estimated at between 30–40 percent of the food supply. Maybe some pet food is wasted as well. Frozen mice are cheap, especially if they are bought in bulk. Owners could be buying more than they need but probably not much more because it takes up freezer space.
  • Force-feeding snakes. Some articles mention that some owners overfeed their snakes because they want them to become bigger.
  • Instead of feeding adults snakes bigger mice, some owners choose to feed them many small mice. This would increase the number of used mice a lot but I haven’t seen much evidence of that happening. However, according to a person with knowledge, the practice of feeding more smaller mice is bad for snake health, hence it is probably not common.
  • Mortality rates during transport and in pet stores.

In the end, even though I don’t trust FBH’s numbers, I don’t trust my estimation in the previous section much either, and the FBH’s numbers are the only direct rodent sales numbers I found.

In the guesstimate model, I use FBH’s numbers to produce an alternative calculation. First I calculate the number of rodents fed to pet snakes in the U.K. To do that, I multiply FBH’s figures (1M–2M frozen mice per week which is 52M–104M per year) by the proportion of frozen mice that are sold as food for pet snakes. As mentioned before, frozen mice can also be used to feed to some other pet animals, and used at zoos and wildlife rehabilitation centers. I don’t know the value of this proportion is, but I guess that it is between 50% and 97%. I then divide it from the proportion of vertebrates produced for pet snake food that is frozen mice. As mentioned before, some snakes are fed rats, chicks, rabbits or other animals but farmed mice seem to be by far most popular, at least in the U.K. Consequently, I guess that the proportion is between 80% and 95%. Finally, I use my estimate that 4–9% of world’s pet snakes are in the UK, to estimate that 540M–2.1B vertebrates are killed for pet snake food in the world each year. Note that I assume that the ratio of snakes to mice in the UK and the world is the same, which might not be correct. Furthermore, I could have incorrectly estimate the proportion of pet snakes that live in the UK.

This estimate barely overlaps with my previous estimate that 85M–320M animals fed to pet snakes per year. This makes me doubt both of my models, so I take the lower bound from one estimate, and upper bound from the other, and end up with a subjective confidence interval of 85M–2.1B vertebrates are killed for pet snake food in the world each year. For comparison, Prize (2014) estimates that around 118M animals are used for experiments, although it claims that this is likely an underestimate. It seems that most of the vertebrates fed to snakes are farmed mice, though I’m not sure what the percentage is, especially outside of the U.K. and the U.S.

Snakes farmed for other purposes

Pet snakes are not the only snakes in captivity. This Business Insider article claims that one Chinese village breeds 3M snakes per year for food and venom (which is used for medicinal purposes). Snakes are also farmed for their skins. I was unable to get an estimate of how many snakes are farmed for other purposes in the world due to the lack of statistics. It’s also unclear how many of these snakes are fed farmed rodents. Here is all the evidence about the feeding of snakes that are bred for purposes other than companionship that I have found:

  • According to Aust, et al. (2016), in China and Vietnam they are usually fed wild-harvested natural food (e.g.amphibians and rodents), waste protein from other industries (e.g., poultry and pork), formulated diets (reconstituted waste protein), and snake meat for King Cobras.
  • This Time Out article about the Chinese village that breeds 3M snakes per year mentions “walking past buckets of dead chicks and frogs used for feeding the snakes.”
  • This news article talks about a snake farm in Thailand that breeds mice to feed them. The practice was called into question by local officials who were concerned that this may violate a newly passed Animal Welfare Act. It’s unclear what was the resolution and whether such practice is common.

Overall, it’s unclear how many of snakes farmed for other purposes are fed farmed mice but it seems that farmed mice is not the most common food for these snakes.

Lifespan of breeder mice

To determine the scale of suffering endured by feeder animals, we need to consider not only the numbers but also how long on average animals live and suffer in factory farm conditions.

Hardin (2013) shows that these rodents can be slaughtered when aged anywhere between 48 hours, to 9 or more months. It also claims that “most feeder rodents typically are sold before or shortly after weaning.” Mice are weaned between 21–26 days of age. Judging from what I see in online stores, I guess that a considerable number of mice are also killed at a different age (both younger and older). A veterinarian told me that at one zoo, some small raptors/reptiles were fed younger mice, but in general, mice were killed (or fed alive) at 8–10 weeks of age

Welfare concerns

In this section, I look at conditions in which feeder rodents live in farms and compare them with the conditions that are recommended for laboratory and pet mice. Then I briefly discuss concerns about live feeding.

This section was reviewed by a veterinarian who wished to remain anonymous. They confirmed my impression that conditions seen in the videos and pictures below are bad. They also told that conditions for feeder rodents they witnessed at a zoo and at a pet store were similar.

Conditions for feeder mice

I’ve only found several videos and pictures of conditions in feeder mice farms:

  • Video 1: a short video of a large feeder mice farm.
  • Video 2: a man explains how he runs a small scale mouse and rat farm
  • Video 3: the video description says that it’s “mice at a farm crammed in a little box before being served to snakes.” Conditions look very bad. Some of the mice seem to be already dead. It’s unclear if these are conditions in which they were grown as well.
  • Video 4: another video that might be representative of how most feeder rodents are raised.
  • Video 5: in the beginning shows how some people may raise few rats for their own snakes in pretty good conditions. Then shows a larger scale farm that is similar to others.
  • Pictures 1 and 2 (see below): I found these pictures at alarmy.com where both of them were titled “White Mice grown for live reptile feed on farm” and uploaded by the same author. Presumably, the first picture shows how one of the containers seen in picture 2 looks inside. The pictured conditions seem very bad.

Picture 1:

Picture 1

Picture 2:

Picture 2

Lack of space

RSPCA guidelines for keeping pet mice explain that “wild mice can have very large territories. Mice need sufficient space to display natural behaviors and give control/choice over their environment.” petsworld.co.uk claims that the minimum cage size for a pair of pet mice is 45cm x 30cm (1350 cm2) with at least 25cm depth.

Fawcett (2012) has these guidelines for the housing of mice in scientific institutions:

“As a guide, enclosures should allow for a minimum floor area of 250cm2 for a single housed mouse, a minimum floor area of 500cm2 for two mice and ensuring a minimum floor area of 60cm2 per additional adult mouse when mice are housed in larger groups.”
“As a guide, the optimal size for a group of adult mice is three to five for females and three for males.”

In video 1 there are 50 mice in a box that seems to be smaller than 1800cm2, maybe even 1000cm2. In some other videos the situation appears to be better, but in video 3 and picture 1 it is much worse.[4]

Living in their own feces

A veterinarian said that in most of the videos a lot of feces can be seen within the bed of all the drawers. Pet mice usually choose a toilet corner, but it doesn’t always happen. I find it unlikely that all rodents pick the same corner when living in such cramped conditions. And even if they do, feces might accumulate quickly. In video 2, the man claims that he cleans containers every “week or week and a half.” According to this page, this might be insufficient even when mice are not cramped.

Lack of shelters

Fawcett (2012) gives detailed instructions for shelters that have to be provided to lab mice. Similarly, RSPCA guidelines explain that “mice are a prey species; they’re highly motivated to stay near cover.” It claims that they need tubes for hiding or sleeping in, shelters with multiple exits where mice could hide when they wish, and avoid any confrontation with other cage mates. In all cases, cages for feeder mice don’t include any shelters.

Living in such cramped conditions without places to hide might be causing a lot of stress to mice, especially if some of them become aggressive. Both, RSPCA and Fawcett (2012) claim that mice should always be monitored to check that cage mates do not become aggressive. I haven’t seen any indication that this is being done in breeding facilities.

Lack of activities

Fawcett (2012) claims that “environmental enrichment is essential for all mice.” Similarly, RSPCA says that “running wheels can be provided but shouldn’t be the only enrichment.” Lack of any enrichment in containers is concerning.

Lack of daylight

RSPCA also claims that mice need natural daylight. However, in all videos, they are only exposed to artificial light and in video 1 they seem to spend their time in darkness.

Possible lack of bedding and nesting material in some cases

RSPCA claims that “mice need bedding material to dig/absorb moisture from urine/faeces” and nesting materials are needed to help body temperature regulation. Bedding materials seem to be present in videos 1, 2, 4 and 5, but they seem to be lacking in video 3 and in picture 1. However, it’s possible that video 3 does not show the environment in which mice spend most of their time. I can’t tell whether nesting materials are provided in any of the videos.

Possible lack of veterinary care

It’s unclear whether rodents receive veterinary care when they need it, but I'd be surprised if they do. A veterinarian said that even when sold as pets, mice are often filthy and don’t always receive adequate medical care.

Lack of regulations (at least in the U.S.)

Hardin (2013) claims:

“Unlike other rodents, rats and mice are not governed by the Animal Welfare Act (USDA 2013) and thus are not subject to federal regulations on caging, transportation and handling. Nonetheless, successful producers generally adhere to professional standards of husbandry. As with any industry, there have been a few operations with unsanitary conditions and substandard care and housing, along with a few unusual incidents, which has cast a negative light on feeder rodent producers. Additionally, feeder rodents have been vectors in zoonotic outbreaks, e.g., salmonellosis, lymphocytic choriomeningitis virus (LCMV), rat bite fever.”

The fact that mice conditions are not regulated in any way makes me concerned. However, in the U.S., no federal laws govern the conditions in which farmed animals are raised either.

Feeding live prey

All the articles I’ve seen advise against feeding snakes live prey. Rodents can injure (sometimes even kill) the snake and cause infections.[5] Despite that, it seems that a significant number of owners are doing it because wherever snake food is discussed, live feeding is discussed as well. I haven’t found any statistics on what percentage of animals are fed alive,[6] but according to Hardin (2013), the majority of animals are sold frozen (rather than live). It claims that this “avoids degradation in the quality of live animals from transport stress.” In addition to stress during transport, animals may suffer while they are kept in a pet store. In this article, a person who used to work at a pet store told that she witnessed ill or injured feeder mice on a daily basis. She told that other workers did not care about their welfare, once dismissing her concern about an open wound because it was “just a feeder mouse.”

Finally, there is also suffering during feeding.[7] As I understand it, most of the time snake will kill prey very quickly. By looking at 20 YouTube videos of live-feeding, Cooper and Williams (2014) estimated that “the time to death as estimated by cessation of any movement was 62 ± 29 seconds for mice, 54 ± 21 seconds for rat”. However, in some cases, snake may not be hungry, and a rodent could be stuck in a tank with a predator for days.

Possible interventions

Here are some possible interventions to reduce the suffering of these animals:

  • Raising awareness about the suffering involved in the raising of feeder rodents amongst the general public could reduce the number of people willing to buy snakes. On the other hand, it might also raise awareness about snakes as possible pets and could lead to more people acquiring pet snakes. Overall, I don’t think it’s a good approach.
  • Raising awareness about the suffering involved in the raising of feeder rodents in the reptile community might be a better approach. It could lead to some snake owners trying to make sure that feeder rodents they buy were bred in conditions that seem acceptable to them.
  • Welfare standards certification scheme. Related to the point above, if we got at least some reptile owners to care about how rodents and other reptile food is raised, perhaps there could be a label that certifies that they were grown in better conditions, in the same way that G.A.P. and other certifiers certify food for humans. Perhaps one of the human food certifiers would be interested in doing this.
  • Improving conditions for breeder mice via corporate campaigns (similarly to the way it’s done in the food industry).[8] It might be a bad idea because such campaigns could make it seem that keeping exotic animals as pets is acceptable, which could increase their quantity.
  • Corporate campaigns that encourage pets stores to stop selling feeder mice and snakes. This petition is an example. General pet stores need the support of general animal lovers, but specialized reptile stores may not care. It could also raise awareness of pet snakes as an option which is bad.
  • Lobbying to ban on the selling pet snakes, or farming animals for pet food. The fact that some animal organizations manage to ban fur farming in certain countries shows that such achievements can be possible. What is more, there are at least some similar laws passed already:
  • Lobbying to ban selling snakes in pet stores, or to display them in pet store windows. Sales of feeder animals in pet stores could maybe be banned with the same initiative. It could decrease snake sales. Similar bans were implemented for other animals:
    • Vancouver banned pet stores from selling cats, dogs, and bunnies
    • Toronto banned the sale of cats and dogs in pet stores
    • There are plans to ban third-party sales of puppies and kittens in the U.K.
    • Displaying dogs and cats in pet store windows was recently banned in Spain. The article claims that “we are certain that it will apply to other animals. For example, maybe fish, spiders, snakes, birds, and more, soon.”
  • Lobbying to increase legal requirements for owning and selling snakes might be possible. In Australia, They seem to be quite complex already. That may decrease the number of pet snakes.
  • Lobbying to limit the number of snakes per owner. This might decrease the number of snakes because some people seem to own very many of them.
  • Enforcement of existing standards. I found four cases of feeder rodents being confiscated due to unacceptable living conditions. One case was in Scotland where, following an inspection by a charity, a man was jailed for contraventions of the Animal Health & Welfare (Scotland) Act of causing unnecessary suffering to rodents he raised to feed his pet snakes. Other three cases are in various U.S. states. One of them resulted in the closing of a farm of about 30,000 mice and an arrest. Conditions for feeder rodents are not regulated by federal U.S. laws, so I’m unsure what regulations were used as a basis of all these confiscations. In any case, there could be ways to make sure that more such prosecutions happen. It would eliminate the worst farms and encourage breeders to ensure less cruel conditions for feeder rodents.
  • Lobbying to have more legal requirements for how feeder rodents are raised. Could be the same requirements as for lab animals. The claim is easy to make: why would we treat animals of the same species differently just because they are used for a different purpose?
  • Encouraging alternative feed sources. Aust, et al. (2016) mentions some farms using reconstituted waste protein. Maybe a small proportion of owners would be open to switching to something like that, but I find it unlikely.
  • Creating an organization that grows feeder animals in very good conditions. It would either sell them at a higher price to owners who care about animal welfare or partly sustain itself from donations.

My intuition is that trying to ban the sale of snakes in pet stores is the most promising intervention, but I'm very uncertain. I also don’t know if any of these interventions would be cost-effective compared to ACE’s top charities.


[1] It also claims that the snake might live for up to 30 years. That means that over its lifetime it might eat over 4K rabbits.

[2] According to AVMA (2012), there are 1.15M snakes in the U.S., owned by 550K households. According to the same source, in 2007 there were 586K pet snakes in the U.S. This 2018 article claims that herps (non-avian reptiles and amphibians) are becoming increasingly popular and mainstream and that sales of their food are increasing. This 2013 Pet Age article claims that “over the past 25 years, the feeder rodent industry has grown substantially”.

[3] Furthermore, I find it hard to believe that there are more pet reptiles than dogs in the UK.

[4] The box in video 3 is tall but as this page (written by a hobbyist) explains:

“tall aquariums are a poor choice, for instance, because mice can't enjoy the space - they need room to run around, not look up at. Not only that, but air circulates poorly in a tall aquarium.”

The page also recommends to use a 20-gallon aquarium for a group of five or six mice.

[5] In a pet store I was told that feeding live mice is illegal in the UK due to animal welfare concerns. If that is really the case, it shows that legislative progress in this area is possible.

[6] According to slide 72 of this presentation:

"34% (83/246) of Minnesota Salmonella cases who reported reptile exposure reported feeding their reptile some type of rodent – 87% (72/83) of snake owners reported feeding them rodents. Among those who fed rodents: – 59% (47/80) fed frozen rodents – 41% (33/80) fed live rodents."

However, this is not a representative sample and live mice may be more prone to cause salmonella.

[7] Cooper and Williams (2014) describes welfare issues with live feeding:

[8] I think that such campaigns could gain public support because the suffering of feeder rodents is more obviously unnecessary than the suffering of animals raised for human food or used for experiments. Non-vegetarians would feel less cognitive dissonance about supporting it. Furthermore, fewer people doubt rodents’ ability to suffer than chickens’ or fish ability to suffer. Rodents are also often featured in campaigns against animal testing which is a cause that has received a lot of attention relative to its size. This indicates that people can care about rodents even if they don’t seem like the most popular animals.


The American Veterinary Medical Association. 2012 U.S. Pet Ownership & Demographics Sourcebook.

Aust P., Tri N. V., Natusch D., Alexander G. J. 2016. Asian snake farms: conservation curse or sustainable enterprise?

Clark, B. 2012? A Report Looking at the Reptile Keeping Hobby, Those Who Want it Banned and Why?

Cooper, J. E., Williams, D. L. 2005. The Feeding of Live Food to Exotic Pets: Issues of Welfare and Ethics

ENDCAP (2012). Wild Pets in the European Union.

Hardin S. 2013. Best Management Practices for Feeder Rodent Production and Distribution.

Prize, L. 2014. A global view of animal experiments 2014.

Fawcett, A. 2012. Guidelines for the housing of mice in scientific institutions.

This essay is a project of Rethink Priorities. It was written by Saulius Šimčikas. Thanks to Daniela R. Waldhorn, Marcus A. Davis, and Peter Hurford for reviewing drafts of this post and making valuable comments.

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An owner of many snakes wrote to me about this article about some inaccuracies. I corrected the article in some places based on what they said. In this article sources on many questions were very poor so it didn’t take much evidence for me to change my opinion. I thought I would also just paste the relevant bits of the email conversation about this (with their permission), in case anyone else was interested in looking deeper into this cause.

Snake owner:  I read your article on rat/mice farms and how the quality of life is bad. Thats not true for some rodent farms but i believe most cases its true. i totally agree with banning all chain stores from selling exotic repitles including snakes. I personally own abandoned snakes from owners. I read your estimates for feeding snakes and its completely wrong. An adult ball python on average eats 1 medium rat every month! Not every week u will make it sick and die. second the corn snake was correct 1 large mouse every 14 days. Your boa one was soo far from reality. As a baby you feed them every week but an Adult eat 1 rat per month!! Any more offten and you are going to make your snake so obesse it will die! So please do your research! I work with a few rescues and do volenteer work on education on exotic snakes and parrots. My personal goal is to educate and make aware how hard to truely care for these animals are, so when i see a well writen and honest document that you wrote up for the welfare of animals that blaitenly ignores basic feeding guildlines to make insaine number for how much these animals eat takes away from your message. Please update your paper with the corrections of feeding quantites. On top of that adult BOAs and adult Ball Pythons only eat once a month dont always eat every month. Most ball pythons go on hunger strikes that can go as long as 1 years without food. So in actual fact you estimate a boa eats 12 rats per year the ball might only eat 8

so Yah your feeding numbers are totally far fetched. Also many other animals eat rats like tegus, savana monitors, hedgehogs eat pinky mice, most lizards.... so its not only about snakes.

Me: Thank you for your message about my article about rodents fed to pet snakes. I am the author of that article but I am by no means knowledgeable on the subject. My numbers of how many animals it takes to feed were based on a couple of hours of googling and are based on sources that are linked. So I agree that they are likely to be off and it would be good to make them better. 

> An adult ball python on average eats 1 medium rat every month! 

Your boa one was soo far from reality. As a baby you feed them every week but an Adult eat 1 rat per month!! 

For ball pythons, my sources are this, this, and this. Each of these sources indicate that they are fed more than one rodent per week. For Boa Constrictors, this page says “Once boas near adulthood, they will thrive while being fed every 10 to 14 days. It is okay to feed your boa more or less often” Could you please tell if you think that these websites are wrong, or if maybe I am misinterpreting them somehow? Also, this page and some other pages indicate that for example, instead of feeding one medium rat, you can feed 2 small rats, or 4-5 adult mice. Do you know if snake owners often choose to feed more smaller rodents instead on one big one? Because that might inflate the numbers.

> Most ball pythons go on hunger strikes that can go as long as 1 years without food.

Interesting, I didn’t know this. Could you tell how snake owners usually react to this? Do they still try to give them rodents every week? If yes, what happens to uneaten rodents? 

The only figure that matters for the final estimation is my guess that on average pet snakes are fed 31 to 94 vertebrates per year. This includes snakes of all ages and species. And this also includes vertebrates that snakes don’t eat who are discarded (if they are actually discarded). If you could tell what figure do you think I should use here instead of 31 to 94 vertebrates per year, that would be very appreciated and I would adjust my model accordingly. Do you think it should be 20? Or 10?

Snake owner: Thank you so much for contacting me on this subject means a lot that you want to get more accurate feeding numbers.

The ball python sources are correct you would be going on the adult feed schedule since they up the feeding quantities very quickly as babies. They grow fast and hit adult in approx. 2 years. They hit their full weight is 3 years but are usually eating their adult food size in 2 years. So, you would be basing the feeding amount on every month Approx. 28-56 days. At that weight if it’s a female 1 medium rat (approx. 4-5 foot) if it’s a small male 1 small rat (approx. 2.5-4 foot) The article is wrong on one point Ball pythons only eat rats since it has a higher fat content. Its also bad to feed multiple rodents over 1 rodent since they get more nutrients out of 1 rodent vs 2 smaller ones.

The boa article is extremely wrong and doesn’t give actual rat size per snake weight. https://oddlycutepets.com/how-often-to-feed-boa-constrictors/ is a much better feeding guide but it does mix up BCC vs BCI. BCC are common boas they only get up too 6-8 foot on average for females and the BCI are true red tail boas they are kept wilder and can often get 8-14 feet for females. Most owners have a BCC boa since they are much easier to handle. In the article it mentions baby-adult and I would recommend quoting the adult feeding since their adults’ way longer (30 years like ball pythons). A boa needs a large to extra-large rat every month or longer as adults they need a bigger meal rather then small meals and less frequently due to the fact, they expand their heart during feeding and require a longer time for the heart to return to normal size. If you feed to frequently you ‘power feed’ this reduces the life span by 15 years. Boas NEVER refuse food and tend to be obese.

For snakes that go on hunger strikes a lot of owners will either have multiple snakes and dethaw less rodents and feed the picky ones first and own a snake that always eats to eat the unwanted ones. If you have one snake you’re trying to feed once a month if the weight remains the same there isn’t any worry. Males go on hunger strikes during the mating season. This can be predictable but hard to judge. Most owners will continue to feed the non-feeding snakes once a month and the uneaten rodents are thrown away since you can’t refreeze them and risk being sick. I personally know friends with tegus that can eat rotten food, so I save them and give them away. For your article assume they are tossed.

There are also milk snakes, corn snakes, king snakes that are the most popular snake in north America. They only eat mice since they need a higher calcium food then a higher fat. These snakes eat more frequently and eat 1 large mouse every 2 weeks. They don’t refuse food and are commonly found obese. They are one of the easiest snakes too keep and commonly labeled as beginner snakes.

https://reptifiles.com/corn-snake-care-guide/corn-snake-food/ is a good food reference for these snakes since they are almost identical in feeding and care. These snakes belong to the colubrid family, which is the largest snake family in the world, they also include hognose and are commonly active during the day. A good reference is if the eyes are round, they are daytime active like us. If the eyes are slitted, they are active during the night like cats. These snakes live 20 years on average the rest mentioned tend to live 30 years.

Hognose snakes are rising in popularity and males get to 1.5 foot on average and females reach 3 foot on average. They eat once every 2 weeks but only eat mice. They can be picky eaters, in the wild they eat frogs and toads and are mildly venomous. They rarely bite and being rear fang venomous they require thawing on the prey for a while but to humans it’s a minor bee sting at best.

https://www.reptilecentre.com/info-western-hognose-snake-care-sheet is a good feeding reference for hognose. Again, hognose can be picky eaters I have mine not eat every once and a while, but I feed them to my corn snake but commonly a would assume they are tossed.

I personally owning 14 snakes, owing 5 species of snakes (children’s python, hognose, corn snake, ball python, and boa) will have to discard 1 or 2 rodents every 4 - 8 months due to only having one animal that eats the larger sized rat. [...]

I’m glad you are bringing attention to these rodent farms and the unethical manner they have in treating the rodents. I personally researched my supplier and found one that ethically treats their rodents and even sells the tamer ones as pets. They kill the rodents but gassing them with carbon dioxide to have a quick death. Also, I would investigate the other prey items such as chicks and rabbits. A lot of snakes prefer quail or small chicks as a food source over rodents and are usually housed in the same facility with the same mistreatment. Also, some people will buy the cheap wild undesired ball pythons and then feed these poor snakes to their larger snakes such as reticulated pythons or Burmese pythons. These massive snakes are commonly illegal in most places since they can regularly obtain 15 -20 feet. [...]

For feeding per year, I would not make a total for all snakes I would break it down to species and then mention that corns, kings and milk snakes meeting the most popular pet snake eating 24 invertebrates per year, and larger snakes eating over average 12. With the larger snakes having a higher waste of uneaten invertebrates per year. Mention that ball pythons notoriously going on hunger strikes having the highest waste of uneaten food, being that they are vastly becoming the most popular pet snake. You can also mention that most snake owners tend to own multiple snakes and that due to the morph popularity have the highest number of discarded snakes with the popularity of certain morphs falling out of popularity.

There is a lot of controversial topics in that, morphs, discarded snakes and owning snakes just based on colour quickly being abandoned.

Again, thank you so much for reaching out to me, I really enjoyed knowing that there is someone speaking out on behave of the massive number of rodents being killed. There is not only snakes but large lizards that greatly consume a vast amount of rodents like tegus or savanna monitors. I know being a snake owner myself looing the ability to own these amazing animals would be a crime but forcing higher regulations for the care of these rodents should be required. Plus trying to restrict numbers of snakes you can own should be also mentioned. I own 14 but only bought 5 the rest were abandoned or rehomed after a pathic 3 years (adult hood) since their cute baby snake is a boring adult or the novelty has worn off.

Me: [...] I already made some changes to my article but I would like to ask you a few more questions if that’s ok. 

1. The most important question I want to ask is this. Do you know at what age most mice and rats farmed for reptile food are killed? I know that it differs a lot, but I need an average for my estimate and I am very uncertain what that is. So if most mice and rats are killed for adult snakes, about how old are they at the time of slaughter?

2.  > "I would recommend quoting the adult feeding since their adults’ way longer (30 years like ball pythons)"

I remember reading somewhere that while snakes can live that long in captivity, many of them don’t due to mismanagement, and that a high proportion of them die after a couple of years. Do you know if there is any truth in that?

3. > "I personally researched my supplier and found one that ethically treats their rodents and even sells the tamer ones as pets."

This gave me an idea of a welfare certification scheme for rodents. Such schemes exist for animals farmed for human consumption, and I may ask those certifiers if they would be interested in something like this. Could you tell what is the name of the ethical supplier that you found?

4. > "Also, I would investigate the other prey items such as chicks and rabbits. A lot of snakes prefer quail or small chicks as a food source over rodents and are usually housed in the same facility with the same mistreatment."

I did mention chicks as a food source. I assumed that chicks that are fed to snakes are male chicks from the egg-laying industry, who are usually culled soon after hatching, as they can’t lay eggs and their breed is not optimized to be grown for meat. If I understand you correctly, you are saying that this is not the case, and that chicks are bred specifically for snake food, right? If that is the case, then I would also appreciate it if you told me how you know this.

Snake owner:

1.Thats a hard one to answer the average size is a medium so they havent reached full size so under a year i would assume im not great on rat ages. Most feeding guides say the sizes but idk the age. Large snakes eat large adult rats. Corn snakes large adult mice.

Average for ball pythons is a medium rat i would estimate under a year old since they arent even full grown.

2.  I would say the majority of snakes do live a full life since an extremely large amount of keepers are generally breeders and experienced owners. For example a new snake owner that window shops is more likely to buy 1. They are the most likely to abandon them. Then theres people like me i own 17 snakes now and most people with a large collection usally spend quite a bit of money on them. Just on speculation i would believe most snakes do enjoy a full life in spite of all the issues you hear. More dogs and cats are abandoned significantly more then any reptile by a massive margin. The difference in snakes espically is they are villanized so they report EVERYTHING.

3.  The supplier i use is called CTC predator. They have top quality. If you dethaw there rats and mice they dont have a smell really. If you dethaw an artic mouse (petsmart brand) they smell terrible and i wouldnt feed them to my snakes.

4. Im really not sure at all where they get the chickens but i assume there males. Most rats are males aswell


There's something about this exchange I find super charming, thank you for sharing. Maybe how kind you both are, trying to help each other, with both of you earnestly motivated by completely different target audiences - you trying to do well by rats and mice, and the snake owner by snakes.

Thanks for writing this up Saulius! I think it is a really useful addition to the literature on EAA. You seem good at writing such content! :)

Some very quick thoughts that I had on this piece:

- My rough impression is that the “pre-slaughter mortality rate” of mice is relatively high. This matches my own experience when I had pet mice when I was younger and a quick google suggests that lab mice mortality seems high. E.g.
> We examined the survival rate of 539 litters of mice from two of the most commonly used laboratory strains (C57Bl/6 and Balb/c) bred under normal husbandry procedures, and found that mortality rate (that is whole litters lost) was at average 28,9%.

- My rough impression is some pet snakes feed on eggs or fish predominantly rather than mice. I am not sure how big a proportion does that though but it could be significant. E.g., I think the Gartner Snake is a fairly common pet breed and that it is common to feed them fish.

- I have a feeling that rodents are farmed in larger numbers for human consumption in some asian countries but a quick google didn’t really confirm or deny that.

- I wonder if more mice are fed to captive/farmed crocodiles, alligators, and caimans then to captive snakes. These other reptiles are are much bigger than the average snake and eat more often, and I think it is common to feed them mice. Skimming this and it seems possible that the number of these other reptiles farmed is in the hundreds of thousands.

-I wonder if mice are fed in quite large amounts to captive predatory birds. E.g., this suggests one of these birds eats x5 the amount of mice p/w than a python does.

- I thinks there’s a decent chance that if one were to dive deeper into the farming of invertebrates then this could lead to discoveries of tens of billions of additional farmed animals the movement largely currently neglects.

But in all I mainly think this is an important area that not many have thought about (including me). Thanks for highlighting it! :)

I thinks there’s a decent chance that if one were to dive deeper into the farming of invertebrates then this could lead to discoveries of tens of billions of additional farmed animals the movement largely currently neglects.

I agree.

Say this is the case, what would be the implications? It does seem that more general anti-speciecism efforts become comparatively more effective the more animal suffering is widely dispersed.

Thanks for working on this! I'm impressed by this and your other work on identifying and investigating groups of farmed animals that exist in large numbers but have been overlooked by other EAs, researchers, advocates, etc.

 I can't count the number of times I've seen folks post on snake groups asking for recommendations for snakes that don't eat rats and mice. It's a serious drawback to what is otherwise an excellent pet. Even snakes that happily eat a diverse diet of fish and insects (garter snakes, for example) still need the occasional mouse in order to not develop a nutritional deficiency. 

There is one breed of pet snake that does eat an entirely vegetarian diet, and it is called the Dasypeltis sp., or African Egg-Eating snake. They're beautiful snakes, but sourcing their diet is very challenging. They require very small eggs as their entire diet. 

The eggs I buy are infertile finch eggs, from an independent finch breeder. In the 8 months since I've owned my egg-eater, she's  had to raise her prices as well as introduce a waiting list due to the breed becoming more popular. 

Figuring out a way to make synthetic finch and button quail eggs with inert, reptile-safe shells would cause this breed to seriously take off, and probably supplant many adoptions of other varieties of snakes.

To whoever was commenting below about reptile pellets, they do exist, but currently they are more expensive than feeder mice/rats, and they're still made of smaller animals. https://reptilinks.com/ 

This is a really good analysis! Thanks for posting.

A few notes I thought of as I read:

  • You state that you're worried about campaigns to stop or prevent snake ownership possibly increasing publicity around pet snakes and increasing their numbers. I think you could try to estimate this effect by looking at similar cases of "negative publicity against a certain pet".

  • For example, when a pet dog kills someone in a way that gets widely reported, do sales of that dog breed tend to go down, or up? Did this story lead to less python ownership in the UK? (These numbers may not be possible to find, but since this question may apply to other CE analyses around pet predators, seems worth a shot!)

  • Since RP is considering interventions to prevent mouse suffering, are there plans to look at changing agricultural policy to protect field mice? This article estimates 6-40 animals killed per acre of grain, per year (seems to be mostly mice), but notes high uncertainty around both the number and the counterfactual outcome for these animals.

  • I didn't see you mention "recommending alternative snakes" as a possible intervention. Even if all the most popular snakes are whole-animal carnivores, I wonder how many people who want to buy a snake would be open to choosing one that eats insects or eggs, rather than whole mice? (I'm not sure how insect/chicken suffering would be affected by this choice, but intuitively it seems less bad than raising so many mice in such poor conditions.)

  • This post is by Rethink Priorities (RP), not Charity Entrepreneurship (CE)! These two organisations are not affiliated. RP does foundational research on neglected causes. CE aims to create high-impact charities.
  • My worry is that many people might not even know that owning a pet snake is a possibility. Any publicity about this issue could make more people aware that they can own snakes, which could lead to increased sales of pet snakes. I don’t know if this concern is valid, it’s based only on my intuitions, and your intuitions are as good as mine here. Everyone knows that dogs can be pets, so the situation is not analogous. Unfortunately, the impact of news stories on snake ownership can’t be evaluated because there is not enough data about snake ownership. There is only yearly data for the UK and it has a large margin of error. In other countries there is much less data.
  • I wouldn’t know how recommending alternative snakes could be done effectively. It may also be difficult to do without sending a message that it’s ok to own pet snakes. And yes, I am similarly extremely uncertain about whether that would be an improvement.
  • One day I’d like to look into changing agricultural practices to protect field mice, it does seem to be an important topic. However, it’s not in immediate RP plans.

Glad you liked the post :)

Edited my reply to reflect the correct organization, thanks!

ok, but I will leave my comment as it is because it seems that many people conflate RP and CE, and maybe some of them will see my comment :)

There is quite a bit of recent controversy about pitbulls, that seems like the right place to start.

I would think the protein substitutes would be a lot cheaper than farmed mice - is that correct? Then it seems like that could substitute for a lot of the non "spectacle of eating live animals" market.

Interesting research. I first became aware of this issue from being involved in the animal welfare movement, specifically with small/"pocket" pets where sale of breeding "overstock" for reptile consumption is sadly common. Unfortunately, some people simply enjoy the spectacle of their pet consuming live prey. More generally, it's part of the broader issue of carnivore pets in general -- the meat produced for consumption by dogs and cats is likely to come from factory farms similar to those raising meat for human consumption, where conditions may be little better than those of the mice pictured here. This has led me to a personal decision to refrain from having non-vegetarian pets, and I know that other EAs have done likewise.

It seems that meat produced for consumption by dogs and cats normally comes from the very same factory farms that produce human food. Because Animals claims that

Pet foods are made from both 4-D meat (animals that are dead, dying, diseased or disabled), and the leftover bits—referred to on pet food labels as “meat by-products”—of slaughtered farm animals. These parts include the snouts, udders, lungs, feet, organs, ears and other parts that humans don’t want to consume.

Of course, this doesn’t change much. Pet food allows meat industry to be more profitable, which leads to them farming more animals. I agree that this is a strong consideration against having carnivorous pets. There was a discussion about it in the EA forum here.

I wonder if outreach to not buy dogs and cats could be more effective for reducing the number of farmed animals than vegan advocacy. And if corporate campaigns that encourage dog and cat food manufacturers to use higher welfare animals (e.g. gestation-crate-free pigs, broilers that are stocked less densely) could be effective.

This is definitely an interesting idea (two interesting ideas, I guess) worth exploring more. I worry though that some issues that might hold up these ideas are (1) these things generally being harder to compare, (2) not having any knock-on / flow-through effects of encouraging better behavior toward animals more specifically, and (3) companion animals being an important influence for people going veg.

Let me know if you'd want to look into this. :)

I agree with you Sir dogs

A natural human tendency is to choose a dog's or cat's food that seems to be 'people's food;' pet owners want to provide dog or cat with the same quality of food they would prepare for each other's family members. Certain pet foods use ingredients such as 'people food,' while others do not. Worse news, pet foods are using human quality and low quality ingredients and pet foods are not as simple as it looks. Pet food rules do not provide any laws or regulations to guide or warn pet owners about higher quality ingredients.

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