Of all the creatures in Hatjörn's dominion, there is none as peculiar as the Murinae Spirita, the mean booze-rat. A vermin so resilient that has developed the most wondrous means of defence and thus survival.

Excerpt from Hjårdan Animaliæ

Welcome to the Most Ingenious Questions You Never Thought Of. Today we look at the booze-rat, an animal aptly named for its unique defensive mechanism of storing strong1 alcohol in its body in order to daze/incapacitate a predator.

In order to do that, one or more booze-rats sacrifice themselves so the rest of the colony can devour the now harmless attacker.
Thus they 'prey' on animals such as cats, weasels and various other predators.

Q: How do the booze-rats produce/procure the strong alcohol in their bodies? And how do they store it so it doesn't hurt/kill them as well?

!!: This question is about finding possible means of producing alcohol inside the body of the animal; and additionally about where to store this alcohol. This question is optionally about finding reasons the animal will not die due to the constant presence of alcohol in its body.
This question is not about how to evolve this animal.
This question is not about the taxonomy of such an animal.
This question is not about if it is an earth-rat nor if it is possible for an earth-rat to evolve into such an animal.

1Strong alcohol: As a household dog/cat will already suffer extremely from a simple beer I assume that some 40-45% alcohol (e.g. Vodka) would probably suffice. But: The more, the merrier!

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    $\begingroup$ +1 -> Can't answer to this, but heck i got a good laugh out of it. $\endgroup$ Commented Sep 27, 2016 at 7:54
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    $\begingroup$ Just leaving this here: en.wikipedia.org/wiki/Auto-brewery_syndrome It's a real thing in humans - who certainly didn't evolve for it ;) $\endgroup$
    – Syndic
    Commented Sep 27, 2016 at 10:42
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    $\begingroup$ @dot_Sp0T The poor things :( . I was hoping it would work like the bombardier beetle. $\endgroup$
    – Skye
    Commented Sep 27, 2016 at 11:46
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    $\begingroup$ "...also known to be extremely flammable, residents have found that throwing a torch upon a colony of booze-rats (a 'booze-cache') to be an exceptionally effective method of destruction. Extermination by this method is not recommended near inhabited areas however, as inflamed booze-rats may ignite wood, straw and other dry fuel. See 'Inferno of Valkind'." $\endgroup$
    – GrinningX
    Commented Sep 27, 2016 at 13:24
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    $\begingroup$ @Konrad Rudolph: I was thinking the booze-rats could filter the ethanol out and store it in their body, probably near the skin so it reaches their predators faster. So the microorganisms would have a comfortably lowish level of alcohol still? Not a biologist here, but I figure if our body can extract nutrients from the slush in the stomach and intestines, THEIR bodies might be able to extract alcohol from it and transport it away ;) $\endgroup$
    – Syndic
    Commented Sep 27, 2016 at 13:37

9 Answers 9


Others have brought up the problem of strong alcohol needing more than just yeast. I'd like to propose a solution to this: forward osmosis through a semipermeable membrane into brine. The latter is relatively easy to produce inside an animal, which makes this considerably more likely than distillation (which would, thinking about it, probably have the nasty side effect that these creatures occasionally explode for no good reason; distillation requires heat).

Article with more details. If someone (who would be doing a bad thing) were to search for the title of this on SciHub, they might find the full text without paying for it.

I'm envisioning a set of organs: a stomach with a very high proportion of amylases (to break carbohydrates, the primary food of these creatures, into simple sugars), a fermentation bladder containing a colony of yeast similar to distiller's yeast (capable of fermenting sugar solutions up to around 17% ethanol v/v), and something analogous to an extra pair of kidneys.

One of these kidney-type organs would remove excess salt from the rats' bloodstream and concentrate it in the tissues of the other, which would need to be specially adapted to cope with that situation. Many animals can rehydrate by drinking seawater using a system very similar to this, only they throw away the salt and keep the water. The second would have a feed from the fermentation bladder, and force the low-percentage ethanol solution through a network of capillaries the tissues of which were impermeable to salt and ethanol, but permeable to water. As the water 'wants' to get to the salt solution to equalise the concentration of water between the two solutions, it moves through the wall and into the brine, leaving more concentrated ethanol behind. With a concentrated enough salt solution, that can result in very high ethanol percentages.

I should stress that this salt would NOT be NaCl, but something more suited - from the paper, "The potassium orthophosphate and pyrophosphate salts can achieve greater final equilibrium concentrations, and at the highest concentration of the pyrophosphate salt solutions can achieve a water activity of aw = 0.24, which is capable of producing a 90% (w/w) ethanol solution"

That means that the rats would need a diet rich in potassium and phosphorus, and suitable enzymes to produce the relevant salts. Good thing they're omnivores, because that means nuts, fruit, and offal, to go with the vast amounts of grain and potatoes (or local equivalent) they need for making sugars to ferment. It also means that if they were cut in half and set alight, they might burn with a somewhat purple flame.

The ethanol could be deposited in vesicles on the skin of the rats, isolating them from it so they're not permanently drunk or dying of liver failure. They would therefore probably be naked rats, or at least look very mangy, and would leave a trail of alcohol wherever they walked in much the same way as our rats leave a trail of urine. That would keep their dens relatively sterile, and allow them to identify trails and locations their kind had been. It would also make lighting a match in a crawlspace with a rat infestation quite dangerous, and licking them (in the manner of toads) a popular pastime.

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    $\begingroup$ I really like the thought of people waking up in midst of the night because a booze-rat blew up, again $\endgroup$
    – dot_Sp0T
    Commented Sep 29, 2016 at 9:13
  • $\begingroup$ Also if you could add some more meat by explaining the methods/findings in the article in your answer I am sure it will easily rise to the top $\endgroup$
    – dot_Sp0T
    Commented Sep 29, 2016 at 9:17
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    $\begingroup$ Expanded, since people seemed interested. It's GCSE-level chemistry and somewhat handwavey 'all these things definitely sort of happen separately in nature' biology. $\endgroup$
    – Xymist_
    Commented Sep 29, 2016 at 9:57
  • $\begingroup$ I can envision the headlines now: "Hipster cafe includes Rat-drippings as signature drink, Heston Blumenthal envious..." $\endgroup$ Commented Sep 29, 2016 at 10:09
  • $\begingroup$ @dot_Sp0T if they exploded as often as your comment suggests they would, they surely would be called boom-rats, not booze-rats. $\endgroup$ Commented Sep 29, 2016 at 20:35

Science Time: How is alcohol created in the first place? The easiest, and more natural way is through fermentation.

"As sugars are broken down by microorganisms for metabolisation (a process where they are converted into usable energy), various byproducts are produced. These "waste" compounds can be either gasses (like carbon dioxide), acids (such as lactic) or alcohols (in the form of ethanol). This is known as fermentation and a key process in the making of antiseptics, preserving spirits and a host of beloved adult beverages."

Now, are there any microbes can metabolise sugars efficiently without being choosy about the conditions in which they do it?

Yeast are small eukaryotes that are found almost everywhere on earth, reproduce at the drop of a hat and are excellent at manufacturing large amounts of alcohol in a very short space of time. Many of these organisms are classed as being anaerobic, meaning they does not require oxygen to live (to metabolise), and so can thrive in environments other bacterium fail to exist in at all. To get the energy they require in these oxygen-devoid areas, yeasts convert sugars into energy through fermentation, producing ethanol as a waste product.

And finally: how does any of this have to do with the rats themselves?

What if the rat's digestive biology (stomach bacteria etc.) included yeasts as a staple organism? The stomach is a warm, dark, hostile and oxygen-lax environment perfect for yeast to cultivate in private, gorging themselves on any sugary materials that come their way.

By giving these rats a second stomach (a cheap goon bag if you will) lined thick with mucus, where in sugar rich foods can be sent and broken down by inhabiting yeasts, a substantial quantity of ethanol will be produced. This alcohol can then be stored safely in this stomach in much the same way HCl is in ours until dissipated, either very quickly through the rear end, or when it is really needed Ie. When the rat decided its time to be a drunken hero!

Through some circulatory/excretory process, when the rat is caught and about to be devoured for the greater good of it's colony, it will release the contents of it's second stomach either into it's bloodstream and main tissue mass (I mean, the creatures already going to die right?) or regurgitate it over itself, so whence eaten, delivers far more than the legal limit of booze into the predator, leaving it chill and mellow to be captured gnawed or whatever, by the rest of the party.

NOTE: The yeast's process of metabolisation also creates carbon dioxide (that makes baker's bread rise), so the rats are going to need to expel much gas during the fermentation process; so the booze-rats will not only be "drunk" in sense, but also be burping and farting a heck of a lot too! How weird would that be: a colony of groggy, flatulent rodents...

ADDITIONAL Q & A: A little off question, but what could attribute to the rats sacrificial tendencies? Is it purely selfless - morally justifiable "cause before self" - or is there some other biological incentive that fuels these creatures actions? The latter seems more plausible (and more widely discussed through the comments - thanks for the feedback guys).

The allure of the ultimate bender is too tempting for most to resist. Seeing as the rats do have their own lifetime supply of booze, it would be safe to assume that they have some degree of access to the alcoholic contents of their stomach (either by choice or because minute quantities of ethanol may be excreted naturally from it over time) and may therefore regularly indulge themselves on such, the rat gradually building a tolerance to ethanol as they grow older, just as some humans do by continually drinking.
Perhaps then, their heroic actions are not so selfless after all, instead simply a means of satisfying their ever growing thirst for ethanol through the biggest hit of booze they will ever have (the entire alcoholic volume of their stomachs being released into their bodies); all the rats would need for this to be achieved are ample dormant alcohol receptors (large untapped dopamine and serotonin stores) in their brains, that can only activated/accessed once the sacrificial pledge is made (hence, once evoked by a huge adrenalin or insulin spike accompanying the release of alcohol). It would not only utterly intoxicate the rodents with feelings of euphoria and unfounded courage, but also act as a pain inhibitor too.

This motive for sacrifice would work to the colonies advantage, for only the rats with a greater tolerance to ethanol - a desperation/drive for more - will offer themselves to a predator; these rats logically will be the oldest drunkards of the colony and so are at greater risk of dying naturally anyway (might as well go out with a bang...). It's this attitude brought on by their tolerance that ensures the younger, stronger rodents of breeding age will live on to reproduce and perhaps even start colonies of their own. Selflessness through selfishness.

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    $\begingroup$ So yeah, the rats will need to be living near sugary foods, such as mangoes, pawpaw or grapes - grapes are better as they naturally contain yeasts in their skins. GO SCIENCE! $\endgroup$ Commented Sep 27, 2016 at 10:31
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    $\begingroup$ As commented above, this isn’t sufficient: fermentation cannot produce strong enough alcohol since such a high degree alcohol will kill the microorganisms producing it. — Distillation is necessary. $\endgroup$ Commented Sep 27, 2016 at 11:57
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    $\begingroup$ @KonradRudolph, you make an excellent point, but then again, we are talking a world where rats have evolved to survive through effectively turning themselves into shot glasses... Besides, by the sounds of things it takes quite a few rats to make a meal for whatever hunts them. $\endgroup$ Commented Sep 27, 2016 at 12:08
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    $\begingroup$ Bonus points if the microorganisms also metabolizes some sort of hallucinogen, that sends the sacrificing booze-rat into a state of extase right before he is about to die. It also adds to the pacifying effect on the predator. $\endgroup$ Commented Sep 27, 2016 at 13:06
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    $\begingroup$ Also other animals can't stand alcohol since they are not used to it. The amount of alcohol we drink is trained by generations of drunk folks making babies. I mean look at the native americans, they get drunk very quick because their ancestors never used to poison them self with alcohol. $\endgroup$
    – Silom
    Commented Sep 27, 2016 at 13:17

I'd guess that the rats eat fermenting fruit and their livers extract the alcohol and diverts it into a special bladder.

Whatever eats the rat will then be treated to an alcoholic hit. It'll be a bit like eating a liqueur chocolate. Several rats may need to be sacrificed for the good of the pack.

They would probably end up being farmed by the local tribesmen and fed on different kinds of fruit for different tastes.


Alcohol is actually a pretty energy dense substance. However, why this would be preferred to simple sugars (which is a typical food source) would be interesting - perhaps the gut flora of the rats efficiently breaks down 'poor' foodstuffs like grass into Cellulosic ethanol. Contrast this with cattle, which need multiple stomachs to digest food - some handwaving required, but it would be an unusual metabolic process.

The rats might 'seem' fat from their metabolic processes, and breaking down large amounts of cellulose to alcohol, stored in their liver, and other body parts.

While typically the maximum percentage of alcohol in solution is limited by how misible it is in water, some processes of natural reverse osmosis or such might be able to increase the concentration of it. Or the creatures might have a tolerance to natural toxins that would increase the effect of the booze on others.

Essentially they eat things nothing else would, to handle mild scarcity, and turn that into a high energy food.

As for one member sacrificing itself - they might have a social structure similar to the naked mole rat. This lets the colony eat, and when food is scarce, they sacrifice themselves to provide a large food source. The drunk 'predator' gets swarmed, eaten and cached. This would have to be rare enough that anything other than the most intelligent predator doesn't catch on though.

  • $\begingroup$ Why would what be preferred to simple sugars? I am not sure I can follow you.. $\endgroup$
    – dot_Sp0T
    Commented Sep 28, 2016 at 9:09
  • $\begingroup$ Simple sugars are easier. Cellulose is hard to digest so there needs to be an advantage to it. Like being a source of booze and meat. $\endgroup$ Commented Sep 28, 2016 at 10:21

Remember there has to be an evolutionary precedent or at least explanation for this.

If the most-alcohol-producing rats are the ones who die, nothing will force their descendants to survive, unless you group the animals in a clade that consists of just their own offspring. This means the rats who survive to breed more will be ones who produce less alcohol and so eventually this trait will breed itself out of the gene pool.

I would suggest instead making the animal a lizard; the alcohol is stored in the reptile's tail and breaks off naturally when attacked by a predator. This allows re-growth of the tail and allows evolution to dictate that the fastest-growing-tails (who can survive many attacks in a lifetime) and the most-potent-booze-makers (who can incapacitate an attacker faster) would be the trends that survive.

It also allows a further explanation for sun basking; providing more energy to ferment the sugars into alcohol. Porous skin that exudes gases as this process occurs could leave the area permanently shrouded in a noxious fog - something that could alert the humans of your story to the presence of these creatures. A coming-of-age ritual where one warrior must claim the tail of a lizard and drink the contents could easily be a plot point.

Again, if there is nothing that forces this development of alcohol production as a primary survival trait, chances are it will never develop far enough to have the effect you want.

Evolution must demand that the alcohol production is a trait that is positively discriminated against.

  • $\begingroup$ You've discussed some great cause-and-effect; I'm imagining a rat giving birth to lizards... I'm going to stop now. $\endgroup$ Commented Sep 29, 2016 at 2:25
  • $\begingroup$ Perhaps then, the alcohol production is not just a means of defence, but of survival... The rats alcoholism may have originally been purely accidental, a consequence of living in a sugar/microbe rich environment for so long. It is logical therefore, that for as long as these rats remain in said location, they will be exposed to fermentation of some kind (eating rotting fruits etc.); it would then make sense for the rats to have a means of coping with/getting rid of the ethanol created, or else they may be poisoned/die due to hyper-exposure, hence their specialised alcohol sacs or whatever. $\endgroup$ Commented Sep 29, 2016 at 4:07

what goes in, must come out...

In most animals unused food matter exits at the rear, however, before it gets there it's broken down into useful components.

For the production of alcohol, we're looking at that wonderdrug sugar.

Your booze rats will have a predilection for sugary sweets, in the wild, this might be sugar cane, sugar beet or various trees broken down for their sap.

Now where to store that boozy poison, in this case, I would have the rats exude the alcohol in all the excretions, like cat dander. They would be immune to the effects of alcohol themselves but their saliva and sweat would cause them to be covered in a dense solution.

The alcohol itself would need a medium, like a waxy discharge to prevent it from just boiling off.

If you wanted to harvest/milk your booze rats, it would then be a case of running a comb through their fur to extract the wax and keeping them in a hot tank to make them sweat more.


Here is on thought on the naming of the "Murinae Spirita":

As far as I understand, Murinae is the name of the Subfamily of "Old world rats and mice". So this word is the name of a large group of different species. However, the Booze Rat is a specific species. So according to the binomial nomenclature, the name of the species should have the following structure:

Genus species.

Genus should be a Latin singular noun in the nominative case specifying the genus of your animal. (I am pretty sure "Murinae" is plural and it is definitely not a genus, but a subfamily.) Examples can be drawn from the article about Murinae, e.g. "Rattus" or "Aethomys".

species can be either an adjective or a noun in nominative or genitive case which specifies the species within the genus. "spiritus" in fact means breath or soul, whereas "aethanolum" would be alcohol and "sucus" is the closest word I could find for liquor.


Before I answer the question, I'd like to point out this:

Alcohol is quite toxic

This imposes some interesting facets to this creature.

Storage: First, it needs to store alcohol in isolated sack and the creature will poison itself if the sack is punctured. This would mean a skilled chef can remove this "toxic" sack from the rat before eating him, like a fugu fish.

Production: Because alcohol is so toxic, it cannot be produced in high concentration by micro organisms. The production slows down and eventually stops as the organisms producing it are killed by it. From top of my head, 15% is the maximum concentration. This rat friend would need a multi-stage process that allows it to concentrate the alcohol it stores. I can only think of distillation and that would be difficult inside a rat. Without concentration, the amount of alcohol stored in a single rat would be too small to pose any significant challenge to the predators.


From wikipedia (https://en.wikipedia.org/wiki/Crucian_carp):

"Crassius species exhibit some remarkable physiological adaptations to their environment. For example, in entirely anoxic conditions during winter Crassius crassius can survive for considerable periods by anaerobic respiration, with ethanol as the major metabolic end product; a facility that is highly unusual among vertebrates. During summer the fish also may survive anaerobic conditions by this metabolic expedient, though only to a far more limited extent; the winter phenotype can sustain fermentation as a substitute for respiration for several weeks on end. Experimentally the fish have been maintained under anoxic conditions for 140 days. Anoxia can be tolerated longest in the coldest water, even down to 0 °C, because colder conditions lower the metabolic rate. Alcohol production occurs mainly in the muscle tissues, but also in the liver, where the process is thought to have originated. Similarly goldfish can produce alcohol in muscle tissues, but to a much more limited extent."


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