# Can a frog be slowly boiled alive without it noticing?

It's commonly believed that a frog will not perceive a rise in temperature, and will boil alive. And, of course, if it were to be put in already-boiling water, it will immediately jump out.

Any truths to this?

No, they don't just hang out in the water until dead. If you think about it this doesn't make sense from an evolutionary standpoint. A frog evolved in an environment where water heats slowly, not where water is suddenly boiling (boiling water isn't terribly common in nature).

• Looks like we need to find a new metaphor, then. Commented Jul 25, 2011 at 21:02
• If I do something for 3 hours, it will be 180 minutes. 180*0.002 = 0.36. Why will the frog die? Because of boring experiments? :) Commented Jul 26, 2011 at 2:14
• @user unknown, oops, it's actually .2C per minute...:) Commented Jul 26, 2011 at 3:36
• "No, they don't. " They don't what? I do not understand to which part of question this relates. Also, would you mind blockquoting the sources?
– Suma
Commented Jul 26, 2011 at 6:12
• @HamandBacon, have you a reference to prove that? Asking people to go off and boil live frogs might be considered a little unethical. Commented Jul 26, 2011 at 16:48

Snopes tackled this myth and the answer is that this is untrue. Although older experiments support this, it's been pretty debunked by modern science.

Snopes quotes a Dr. Victor Hutchison, Research Professor Emeritus from the University of Oklahoma's Department of Zoology:

The legend is entirely incorrect! The 'critical thermal maxima' of many species of frogs have been determined by several investigators. In this procedure, the water in which a frog is submerged is heated gradually at 2 degrees Fahrenheit [about 1.1 degrees Celsius] per minute. As the temperature of the water is gradually increased, the frog will eventually become more and more active in attempts to escape the heated water. If the container size and opening allow the frog to jump out, it will do so.

• The whole "debunked" meme is basically slanderous in science. It implies not just that the previous science was wrong, but that it was garbage and/or fraudulent to begin with. It's unnecessary rhetoric that degrades science, which is all about continual improvement, and can only happen by our predecessors being wrong in some way. Calling it "debunking" devalues the important work predecessors contributed. Science is about building on the past. Debunking is the politicization of science. Commented Jul 25, 2011 at 21:53
• Wow, I did not realize the word had such connotations. I always figured it just meant it was later proved wrong. Commented Jul 25, 2011 at 22:27
• @AgentKC - you are right. de·bunk/diˈbəNGk/Verb 1. Expose the falseness or hollowness of (a myth, idea, or belief) - sure, science improves, but it is blatantly obvious that for earlier scientists to claim this myth was true, there must have been something going on... Commented Jul 25, 2011 at 22:40
• @Rory Alsop -- Dictionaries don't always cover current social connotations and implications of words. However in this case, at least some do if you don't cherry pick your definition: Via Dictionary.com, first definition -- "to expose or excoriate (a claim, assertion, sentiment, etc.) as being pretentious, false, or exaggerated". Commented Jul 26, 2011 at 13:33
– Erik
Commented Mar 15, 2017 at 20:29

Despite a few modern scientists claiming the boiling frog tale is completely implausible, they're most likely wrong, if you allow some flexibility of interpretation.

Firstly, boiling water is fatal for a frog, so it may or may not even manage to jump out before dying. Secondly, being partially submerged in water that's 40 °C for enough time is already sufficient to "boil a frog alive", in the same sense you might call dying in a 60 °C hot spa "being boiled to death" even though the water is nowhere near boiling. So the question is, can you have a frog sitting in cold water and heat it to 40 °C without it reacting and escaping before it dies?

According to several 19th century experiments performed by at least three different people, the answer is yes, if the heating is gradual enough. If we place our trust in previous results, whether performed in the 19th century or within the last two decades, what we can conclude is this:

• Heating at 3.8 °C per minute, a frog violently attempts to escape. [Goltz, 1869]
• Heating at 1.1 °C per minute, a frog attempts to escape. (Our modern scientist Hutchison makes this claim, which is probably true, but he never performed this experiment personally as some people imply.)
• Heating at 0.2 °C per minute, a frog sometimes dies without ever moving, assuming it doesn't get distracted by other external disturbances. [Heinzmann, 1872; Fratscher, 1875; Sedgwick, 1882]

Several modern scientists (some of which are amphibian experts) have claimed the boiling frog tale is a complete myth. However, none of them have ever replicated those experiments at that gradual rate of 0.2 °C per minute, which Heinzmann started at about 21 °C and ended at ~38 °C after 90 or so minutes. In all probability, none of them performed any experiments when consulted on the matter. One can infer that Zug, Hutchison, and Melton have probably never heard of those 19th century experiments, and certainly not read them (a few of them being in German). Kruszelnicki has heard of Heinzmann's result, but only based on an incorrect citation of Heinzmann by Scripture [1897], and Kruszelnicki is clearly ignorant of the fact that the water need never reach anywhere close to 100 °C. Pechmann (also ignorant of the 19th century experiments) was the only modern biologist to admit that he didn't and couldn't know the answer without an experiment being performed. Most of these scientists were contacted for their comment in response to a query from a member of the public, so it's giving them far too much credit to assume that they looked into it seriously.

What is it more plausible to believe:

• That these casual opinions from modern scientists, despite no experiments or specific evidence in their favor, should be trusted completely?
• That Heinzmann's publication detailing no less than 27 experiments on the muscle reflex of frogs in relation to temperature, not to mention replication by Fratscher and numerous other similar experiments being performed by others around the same time, probably weren't completely made up and invalid, especially given that the boiling frog tale didn't exist at the time and that they were investigating something a bit more involved than that?

If you want more information, I've pretty much read about all the relevant sources on the topic, including all of the modern claims, the papers by Sedgwick and Heinzmann (although in German), Scripture's book. I have a summary of why the modern claims don't disprove anything.

References:

Goltz, F. L. (1869). Beiträge zur Lehre von den Functionen der Nervencentren des Frosches. A. Hirschwald.

Heinzmann, A. (1872). Ueber die Wirkung sehr allmäliger Aenderungen thermischer Reize auf die Empfindungsnerven. Archiv für die gesamte Physiologie des Menschen und der Tiere, 6(1), 222-236.

Fratscher, C. (1875). Ueber continuirliche und langsame Nervenreizung. Jenaische Zeitschrift, NF, 11, 130.

Sedgwick, W. T. (1882). On variations of reflex-excitability in the frog, induced by changes of temperature. Stud. Biol. Lab., Johns Hopkins University, 385.

Dr Karl commented on the original German experiments:

Or perhaps the story began with E.M. Scripture in 1897, who wrote the book, The New Psychology. He cited earlier German research: "…a live frog can actually be boiled without a movement if the water is heated slowly enough; in one experiment the temperature was raised at the rate of 0.002°C per second, and the frog was found dead at the end of two hours without having moved."

Well, the time of two hours works out to a temperature rise of 18°C. And, the numbers don't seem right.

On the other hand, while the Straight Dope is doubtful, it believes that the evidence could be better:

Getting back to boiling, modern commentators agree the results claimed by the German researchers are preposterous. However, no one to my knowledge has attempted to precisely replicate the earlier work, possibly because they haven’t read the studies, which are written in (duh) German. In the experiments I’ve come across, researchers have placed frogs in water and heated it relatively quickly till the frogs jumped out, failing to recognize that the point of the exercise was to heat the water gradually. (Typically the gas gets turned up at a rate of two degrees per minute, about six times faster than Heinzmann did it.)

They also claim that a similar experiment was done with crushing the feet of a frog:

On a related subject, psychologist Edward Scripture in 1897 noted a grisly experiment where a frog’s foot was clamped in a screw press that was tightened at about a thousandth of an inch per minute. Result: the foot was completely crushed without the frog showing any distress. Somewhat worryingly, the author wondered what could be accomplished using humans rather than frogs.

• According to another source, Die Zeit, a german newspaper which names a Scientist from the University of Oklahoma, Victor Hutchinson, the blood of a frog stalls at about 40°C. So the water could be heated up from 22°C in that timespan to a lethal temperature. Of course it wouldn't boil. Commented Jul 19, 2014 at 4:08

Sorry to disappoint, but the "boiled frog" phenomenon is an "old folk warning". This essentially negates your original question altogether. Neither a cold-blooded animal (such as a frog) or warm-blooded animal will boil to death under the conditions implied by the warning (i.e. escape is permitted and water is heated very gradually).

1897 research by German scientist E. W. Scripture, upon which the fable may have first been based, has been deemed flawed by scientists:

From Scripture's research: “. . . a live frog can actually be boiled without a movement if the water is heated slowly enough; in one experiment, the temperature was raised at the rate of 0.002 degrees Celsius per second, and the frog was found dead at the end of 2.5 hours without having moved."

According to Dr. Karl S. Kruszelnicki (Australian scientist): "[T]he numbers just don’t seem right. If the water comes to a boil, that means a final temperature of 100 degrees Celsius. In that case, the frog would have to have been put into the water at 82 degrees Celsius. Surely, the frog would have died immediately."

According to Dr. Victor H. Hutchinson (Herpetologist and Zoology Professor at University of Oklahoma): "The legend is entirely incorrect! The 'critical thermal maxima' of many species of frogs have been determined by several investigators. In this procedure, the water in which a frog is submerged is heated gradually at about 2 degrees Fahrenheit per minute. As the temperature of the water is gradually increased, the frog will eventually become more and more active in attempts to escape the heated water. If the container size and opening allow the frog to jump out, it will do so."

Whit Gibbons (University of Georgia) says that there is an important message behind the false legend:

So where does that leave us with the boiling frog as a metaphor for the human response to economic change or environmental degradation? Well, it's not true that you can induce a frog to willingly remain in boiling water by starting it off in cold water. But that does not diminish the truth of the message that the accumulation of imperceptible changes can have a significant effect on the economy and the environment. We need to be aware of what changes are occurring and to respond to them in a timely fashion. The metaphor lies in the frog's ability to escape from the container: if there's no way out, then the frog's fate is a foregone conclusion.

There are 2 important points in the story which are important, one is plain wrong, the other one is heavily disputed.

According to the german weekly newspaper Die Zeit, which names a Scientist from the University of Oklahoma, Victor Hutchinson, the blood of a frog will stall at about 40°C (which is about 104°F) and kill the frog. So every Story in which the frog is slowly heated until boiled must be wrong. Of course it could be the wrong version of a true message, which has moved through too many stations.

The second observation is, that a frog will escape heated water already at 25°C. But there are different investigations with different findings, which heat the water at different rates.

With the name of Victor Hutchinson from Die Zeit, I found a whole Wikipedia article with many sources.

Friedrich Goltz demonstrated that a frog that has had its brain removed will remain in slowly heated water, but an intact frog attempted to escape the water when it reached 25 °C.

But

An 1872 experiment by Heinzmann demonstrated that a normal frog would not attempt to escape if the water was heated slowly enough

Goltz raised the temperature by 3.8°C per minute while Heinzmann heated with 0.2°Cpm.

Other sources talk about 0.002°C per second, which is 0.12°Cpm.

In the end, the article mentions modern scientists, Professor Douglas Melton, of the Harvard University Biology department, Dr. George R. Zug, curator of reptiles and amphibians at the National Museum of Natural History and Dr. Victor H. Hutchison, Professor Emeritus of Zoology at the University of Oklahoma, but only mentions their opinions, not research or papers. They all agree that the frog will flee.

• I would think it very plausible that 0.12C/min could yield very different results from 3.8C/minute. At the latter rate, I would expect the water temperature would be consistently hotter than the frog's core temperature, but at the former rate, it might actually be cooler than the frog's core temperature (even though frogs are cold-blooded, I would think their metabolism must produce some amount of heat). Certainly experiments performed with the faster temperature rise should not be regarded as disproving claimed results with a slower rise. Commented Aug 21, 2014 at 22:50