We know the zombies have a fairly simple existence, they can only perform basic functions (like walking) and only care for eating flesh. Yet in the Walking Dead series literally years are passing since the first outbreak and these zombies are still active. Wouldn't their brains eventually die due to low glucose levels or something?

So even if the zombies are still active years later, why so many of them? We know there are other groups in the Walking Dead universe constantly killing lots of zombies every day, at a pretty good rate. Is this ever explained?

  • 8
    WTF? Zombies're always dead. You say they're brainles and then ask "wouldnt their brains eventaully die?"
    – Octopus
    Commented Jan 9, 2015 at 8:04
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    If they are always dead, then why are Rick and friends constantly trying to kill them? Commented Jan 9, 2015 at 8:05
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    Welcome to Sci-fi Stack Exchange! It sounds to me like you're asking two questions: "why don't zombies 'die' on their own" (i.e. why don't their bodies deteriorate to the point where they stop being a threat) and "Why are there so many zombies if survivors are killing them so frequently." I suggest you either focus your question a bit or split it into two. Also, the question is a bit hard to read with missing words and such. Might want to clean up the question while you're at it. Commented Jan 9, 2015 at 8:19
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    Also, Why do the Walking Dead zombies stop decomposing? has already been asked and received some good answers, so you probably want to revise your question so yours is not a duplicate. Commented Jan 9, 2015 at 8:28
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    Killing and destroying are two different actions.
    – Brian S
    Commented Jan 9, 2015 at 15:10

9 Answers 9


They do

In Letter Hacks #14 and #111 it's stated Zombies eat for impulse and posess no functioning digestive system, with what they've eaten being forced out once its full, unprocessed. It's not required for their sustained animation.

Robert Kirkman wrote on Reddit: ...In the beginning of the show we saw walkers do things like using a rock to help bash the doors in or turning a door knob, is there a reason we've stopped seeing them do that?

"Older zombies are less together and capable or doing things like that. Fresher zombies, which there were more of in season one, are able to do more than older, more rotted zombies.

The worse state of older zombies holds the key; when a human starves, the body will break down fat, then muscle, followed by vital organs. The slide in mental function seems to imply the parts of the brain stem re-animated are canibalized in the process.

Since zombies do not digest, this would be how they survive, and the slower decay that stops them being a bare skeleton in a matter of a few weeks,(#9 and #11) could easily be the virus' way of preserving and stretching its 'food' source.

They would end up running out and 'starving' (in a manner of speaking), but there is no indication of how long, other than that that a surviving human would most likely outlive it, through the years, and that a zombie's lifespan would differ depeding on the individual, (#7); which makes sense, given body fat ratio, muscle density, state of organs and tissue changes from person to person.

Zombies do die off of their own accord, albeight slowly, and it happens whether they eat or not.

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    This is awesome, can't believe there's an answer that actually makes sense! Commented Feb 17, 2015 at 19:41
  • More troublesome to me is that whatever animates the zombies, its not related to oxygen chemistry. Their circulation is null, they can not bleed out. You see zombies trapped underwater continuing to flail around. Now I know WWZ addressed this issue by having the pathogen transport oxygen bypassing the circulatory system. But it would seem to me that should make the zombies quite flammable with all the extra O2 on board, so I never really bought it
    – infixed
    Commented Nov 7, 2016 at 17:57

I'm going to address the second part of your question, since the existing answer took care of the first part.

So even if the zombies are still active years later, why so many of them? We know there are other groups in the Walking Dead universe constantly killing lots of zombies every day, at a pretty good rate. Is this ever explained?

The Kill Count Prior to Season Five:

There are statistics for zombie and human deaths on the show up to the end of season four. This site lists the kill count in seasons 1 through 4; I don't know if their numbers are exactly right, but assuming that they aren't wildly inaccurate, they are good enough for our purposes. I have taken the liberty of breaking down the data and creating a spreadsheet.

enter image description here

The members of the group who are listed by name in the chart have killed 956 zombies and 39 people. Other human characters have killed 229 zombies and 136 people. Zombies have killed 78 people.

The grand total:

1,185 zombies killed

253 people killed

In the comic books, and to a lesser extent on the show, Rick's group are depicted as being among the best fighters left in the world. They have repeatedly fought off much larger forces of zombies and bad guys alike. In comparison, people who aren't in Rick's group are usually zombie fodder.

The first four seasons of The Walking Dead represent perhaps 2 years of time. In 2 years, the best zombie killers around have only managed to kill 956 zombies. This does not bode well for humanity.

How Many People Versus How Many Zombies?

The blurb for the tenth issue of the comic book says:

After the ordeal Rick has endured last issue, he sets out to find safer shelter. More is learned about the zombies that now out-number us 5000 to 1, but when it comes to some things, it's better not to know. Rick begins to wonder if there is a light at the end of the tunnel his life has become. Even if there is, how can he ever expect to make it there?

In Issue #10, Carl is brought to Herschel's farm for the first time, having just been shot by Otis. This corresponds to the second episode of Season Two of the show. The second episode of Season Two takes place about a week after Rick wakes up in the hospital, and a few weeks since the outbreak began.

This means that within weeks of the beginning of the outbreak, only 0.2% of the population was still alive. What does this mean?

0.2% Humans, 99.8% Zombies:

  • Worldwide: 1,400,000 people against 6,998,600,000 zombies.

  • United States: 60,000 people against 299,940,000 zombies.


We're doomed, and trying to survive is just playing for time.

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    Assuming the group represents average ability to kill zombies per person, and roughly 25 people in the group at one time or another by the time i stopped watching, and based on your estimate of 1000 zombie kills, 3 million non-zombies and 297 million zombies. This would average 40 zombie kills per person. At 3M people, this would be about 120M zombies dead and 177M zombies still alive. This would likely be an over estimate of kills, as many of the initial non-zombies were (probably) killed before they knew how to fight back. Conclusion: we might not be totally doomed, but if not, we're close.
    – atk
    Commented Aug 6, 2015 at 15:03
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    Oh, my intention was not to disagree with you! I just thought it was an interesting extrapolation for the data at hand. My comment was something a 'best' case scenario (though, admittedly, not well described as such). We could probably extrapolate further, based on the 'best in the world' statement, if we were to put them as an example of the 100th percentile of a bell curve... but i suspect that would be more ofa fun paper than a comment ;-)
    – atk
    Commented Aug 8, 2015 at 1:04
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    @atk - No worries, I didn't think you were disagreeing, I just wanted to point out that Rick's group is not representative of the average survivor. I doubt that anyone is as deadly as Rick's crew, so their record is unusual and can't be taken as an indication of how many zombies the average person could kill.
    – Wad Cheber
    Commented Aug 8, 2015 at 1:21
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    @MissMonicaE - Without spoiling anything beyond "The heroes of the comic always win, with or without losing some important people in the process", the comics show the group repeatedly coming into conflict with increasingly powerful human enemies, like the Governor, the cannibals, and Negan. Rick's side always wins. So we can safely say this: "Rick's group, however big it is at the time, has never lost a war with another group, even when the bad guys outnumbered the good guys. They lose some battles, and some of them get killed, but they always win the war."
    – Wad Cheber
    Commented Nov 16, 2016 at 0:42
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    Con't - Rick's group is also clearly as skilled as anyone could be at killing zombies. Individuals, like the Governor or Negan, might compare to the abilities of Rick and co, but we never see a group comprised almost entirely of people who operate at this peak level. Last season (and earlier in the comics), we saw Rick's core team, plus a couple of Alexandrians, wipe out an entire herd of hundreds of zombies at close quarters, with little or no use of guns. Ezekiel and the Kingdom have a few people this good. Woodbury had less than 6....
    – Wad Cheber
    Commented Nov 16, 2016 at 0:49

The olm, an amphibian, can survive a decade without eating while remaining mostly inactive, yet conscious. Because cold blooded animals can burn next to no calories during inactivity, we need to look at how much energy is available for useful activity.

Calories/Mile: A human being burns ~70-100 calories per mile while walking slowly. https://www.verywell.com/calories-burned-while-walking-3432716

Calories Available: Tissue in the human body possess ~81,500 calories. http://www.popsci.com/article/science/ask-anything-would-cannibalism-make-you-fat

Results: 81,500kcal/(85kcal/mile) = 958 miles Obviously a zombie can't walk if it has no body, so lets assume it can burn 50% of its mass. 958/2 = 479 miles

A zombie should cease to be active after travelling 479 miles.

  • This is an interesting answer, but could be improved with citations to the claims that a human being burns ~70 calories/mile and that tissue in the human body possesses ~950,000 calories.
    – Null
    Commented Feb 29, 2016 at 17:32
  • Thanks for the suggestion Null, I also discovered that kcal and calories are the same unit, my previous calculations were very wrong.
    – ishannon
    Commented Feb 29, 2016 at 21:40
  • Assuming of course that they're not powered by evil.
    – DCShannon
    Commented Apr 4, 2017 at 22:25
  • Don't forget to account for the calories our brain consumes! Zombies only use a few neurons like primitive animals like jellyfish
    – ericn
    Commented Jan 3, 2020 at 2:09

Zombies should logically terminate / decompose after too much time with no nourishment. The tissue on them would degenerate up to the point where they can no longer have enough of it to be able to move and then up to the point where only the bones remain, practically making them re-dead. Permanently.


If the virus prevented bacteria, molds and fungi from decomposing the host body. Then it is conceivable that a zombie's body could last for a much longer time. Look how long a McDonald's hamburger takes to decompose.


Zombies in the show should definitely die out with time. It's entirely unrealistic that they wouldn't (Assuming they don't reproduce).

The virus takes over a human body, hence no matter how potent, it still needs to fulfill the living requirements of a human to keep control over its husk.

Some people said the digestive system shuts down, that's great, it explains why the stomach doesn't eat itself, but it in no way sheds light on why they don't need food.

Zombies clearly make use of muscles to get around, they have control over the brain, which implies at least some parts of the nervous system are still being used. They also have red blood, which means the liver and heart are both there to purify and pump respectively. Blood is also an essential requirement for the transportation of oxygen (So lungs work too) to the brain, and nutrients to the muscles. It is for instance entirely unrealistic how The Governor kept zombie heads in his aquariums, which then started moving when the aquarium broke. They would have been dead from lack of oxygen, as brain cells die without it. In fact, to indulge this tangent, the fact that the virus takes over minutes and hours after death is unrealistic, as by that time the brain would have suffered considerable injury (brain cells do not regenerate).

All of this to say, human muscles require oxygen and nutrients to work, that's non debatable, hence zombies need a constant intake of food, and additionally they need a digestive system to break the food down into nutrients. Without this process, they'd die very quickly.


1) The survival of zombies is not scientifically possible for long periods of time no matter how potent the virus is that makes them animate. Since the zombies are obviously decomposing which means there is no regeneration of cell tissue which means no repair to wear and tear which means their feet should have scrapped off long time ago and subsequently the leg bones would snap and be useless for travel. Recent episodes show mummified like zombies but the mummification process would entail lots of dry heat and very little humidity - not a possibility in the southern u.s. 2) No matter how many zombies are destroyed/rendered brain dead, you must take in account the sheer numbers of billions of them. Herds migrate and even if you kill a large city full, there are more cities of them coming.


Obviously there has to be some suspension of disbelief regarding zombies, so some questions just don't have logical answers. Muscles can't work without a fresh supply of oxygen, so that means walking is impossible without a functional circulatory system. Dead tissue, left out in the open, would rot in a matter of weeks or months (you can see time-lapse videos on YouTube of various dead animals decaying).

Having said that, I would point out that Walking Dead was never about the zombies anyway. :)


In wood bury brians henchman studied the process of the walkers the best he could he is asked do they starve? N he says yes but they do it much slower then us and if your dead your rotting so over time yes the herds will dwindle in numbers

  • You could provide a transcript and an episode number to make this a better answer. Commented Apr 4, 2017 at 19:09

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