The dragons in my fantasy world spit fluid from their mouths when threatened, which upon contact causes a burning sensation. I could have this liquid be standard venom, like modified saliva, but I wanted to shake things up a bit.

Could powerful stomach acid be spat as a means of defense and/or attack? My main concern is that it would be either too inefficient or too evolutionarily unlikely that another method of defense would be much more plausible to evolve.

I'm not aware of any duplicates to this question, apologies if I've missed one.

  • $\begingroup$ I see you're sneaking in three extra questions there ... best practice is to ask one focused question in order to get one good answer. You can always ask follow up questions. But you knew that already! Please edit accordingly. $\endgroup$
    – elemtilas
    Apr 15, 2019 at 16:45
  • $\begingroup$ @elemtilas Fair enough. Question edited. $\endgroup$
    – SealBoi
    Apr 15, 2019 at 16:48
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    $\begingroup$ Great! Question answered! $\endgroup$
    – elemtilas
    Apr 15, 2019 at 16:55
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    $\begingroup$ Related (but not a dupe): worldbuilding.stackexchange.com/q/115804/21222 $\endgroup$ Apr 15, 2019 at 17:04
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    $\begingroup$ As another alternative, consider the Bombardier Beetle: en.wikipedia.org/wiki/Bombardier_beetle $\endgroup$ Apr 15, 2019 at 20:16

3 Answers 3


Could powerful stomach acid be spat as a means of defense and/or attack?

YES but...

The stomach of any organism using acid as digestive liquid is protected against the action of said acid by a thick layer of mucus. The esophagus doesn't have the luxury of this layer, and is thus much more vulnerable to the action of the acid. In fact humans can get esophagus perforation in such cases.

So, if you want your dragon to throw up acid, you need to coat its esophagus with a thick layer of mucus.

However... attacking after lunch would mean emptying one's stomach, which would result in a energetic loss. It is reasonable as a mean of "better hungry and alive than full and dead" for a lesser animal, but for a might dragon might be a bit against the rule of cool.

Better would be to have your dragon develop some pockets where acid can be stored and used at necessity, without the need to throw away a well deserved meal.

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    $\begingroup$ Presumably, this attack would be used as a means of acquiring lunch, so that would not be a problem. (It would even pre-digest your food a bit before swallowing it...) $\endgroup$ Apr 15, 2019 at 20:49
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    $\begingroup$ Also, the acid could be produced/stored in glands or bladders located just above the stomach along the esophagus; they could have an extra sphincter in their esophagus -- one above the acid bladders in addition to the one below. Normally, when digesting, the upper one closes and the lower one opens, and the bladders secrete a small portion of their contents to help digest food. When the dragon needs to spit though, the lower sphincter closes while the upper one opens, and the bladders disgorge a much greater volume of acid, creating a nasty acid spray. $\endgroup$
    – Doktor J
    Apr 15, 2019 at 21:28
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    $\begingroup$ @DoktorJ at which point you're basically replicating the spitting cobra except spitting acid instead of neurotoxins. And the cobra has a better mechanism as it doesn't have the stuff flowing through his body in places that could be damaged by it. $\endgroup$
    – jwenting
    Apr 16, 2019 at 5:18
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    $\begingroup$ Lots of creatures have more than one stomach. Top stomach empties quickly after a meal. (An acid bladder similar to the mammal gall bladder is a more elegant solution though.) $\endgroup$
    – arp
    Apr 16, 2019 at 14:19


Gastric acid (HCl) can be used as a means of defense or attack. Acid weapons are known in nature. Ants spray formic acid, for example. Some birds, vutlures for example, vomit as means of defense. A number of creatures evert their stomachs in order to clear out yucky things they've eaten.

In the literature, we find this example of gastric acid magic.

enter image description here

Yum. So yes, your dragons could certainly do this as well. If they're large beasts, the effects will probably be quite astonishing.

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    $\begingroup$ Additionally, depending on the diet of the dragon, the acid may have to be more corrosive in order to digest exotic items. This makes sense in an evolutionary perspective. $\endgroup$
    – Mathaddict
    Apr 15, 2019 at 16:56
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    $\begingroup$ @Mathaddict Indeed! If you look into vultures as a real world exemplar upon which to model the dragon's behaviour, their gastric acid is terribly acidic compared with humans'. $\endgroup$
    – elemtilas
    Apr 15, 2019 at 17:04
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    $\begingroup$ Love those "Would this crazy outlandish thing be possible somehow?" "Yes, it already exists in nature." $\endgroup$
    – Eth
    Apr 15, 2019 at 17:08
  • $\begingroup$ Also bear in mind that evolutionary pressures could mean it's developed additional acid producing glands to generate extra acid for spitting (i.e. they may not need to vomit to achieve the same effect). And a creature that's evolved to do this will likely have also evolved a way to protect its esophagus from the acid (excess salivation, mitigating compound secretion, etc.). $\endgroup$
    – KenLFG
    Apr 17, 2019 at 22:27

Stomach Acid

As others have stated, yes you could use stomach acid as a weapon. I would agree with L.Dutch though that they would likely have dedicated acid stacks rather than using the acid in their stomach for practical reasons. (Perhaps acid is produced and stored in these sacks, one tube leads to the stomach to fill the stomach with acid, another tube leads up towards the dragon’s head). You would need some kind of protection against the acid in the mouth, acid sacks and the tubes leading to the stomach and mouth.

If you wanted to get a bit fancier, rather than just having a tube in the dragon’s mouth that ejects the acid, you could have the tube run up to some fangs. This way you could have your dragon either spray out the acid or inject it into their prey.

Super Acids

Rather than just using plain old stomach acid, we might be able to do one better. By combining various acids, we can create one which has a negative PH level. You may be able to have two different acids produced and stored in separate sacks. When the dragon wants to use it as a weapon, some acid from each sack is ejected, causing them to mix. Now, i don’t know of this would be biologically possible as i’m not certain of the manufacturing process of super acids, however if it is you may want to consider this.

Digestive Enzymes

Instead of using acids, you may want to use enzymes. Whilst acids will burn someone they might not break down fats, which makes up a large portion of an animal’s body. However, if you instead fire out enzymes that break down a creatures body, it would likely cause the burning sensation you are after whilst also pre-digesting a dragon’s food to some degree.


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