Written by 1LT Chris Post

One of the greatest determiners in how long the coming zombie plague will last is the lifespan of zombies themselves. In theory, the length of any outbreak will depend on how long individual zombies are capable of moving about and spreading their infection to new hosts.

Because zombies occupy a limited, rotting corpse, the real question then becomes: How long will it take for the zombie to decompose?

Decomposition is a process whereby plant and animal bodies are broken down into their base materials. The length of this process is affected by several factors, including:

  1. Presence of insects
  2. Microbial activity
  3. Moisture levels

I’ll focus on microbes and moisture in upcoming posts, but today I want to talk about insects.

Insects, specifically carrion feeders, play a vital role in decomposition, as they consume much of the flesh and soft tissue of a corpse. In fact, it has been documented that in some parts of the world dense insect populations are capable of reducing a body to bones in a matter of hours.

Assuming a zombified corpse is essentially the same as a standard corpse, insects would feed on the zombie’s flesh and organs, speeding up decomposition and reducing its lifespan. However, a few variables might play a part in mitigating this process:

  • MOVEMENT: The zombies own movement might serve to keep some insects at bay. One need only observe the common housefly to see that they will retreat from the slightest wave of a hand.
  • INEDIBILITY: Whatever causes the reanimation of the zombie corpse might render it inedible to insects. Without the assistance from insects, decomposition time could be extended significantly.
  • PSEUDO-LIFE: Larval parasites, such as maggots, do not eat living flesh. Maggots have historically been used to clean wounds because they only eat dead tissue, leaving the living flesh intact. If zombies have some residual life functions, such as circulation or respiration, it might be sufficient to prevent the maggots and other similar parasites from consuming their flesh.

Look for more observations about zombie decay, including a detailed breakdown of how microbes and moisture could save the human race, in parts 2 and 3 of this series.

Lieutenant Post is a squadron safety officer with the United States Air Force Auxiliary. In addition to training in emergency response and disaster preparedness, he has studied the theory and science behind the zombie of popular culture for several years.


  1. Edward Cornett, DO. FAAEP

    1.Zombie decay states are found in 3 distinct physical stages:

    a. Fresh state: recent transition into the phenomenon of Zombotic existence. Mild livor mortis or “lividity” is seen in their general appearance at this stage in their life cycle. Muscular rigidity is present[rigor mortis] which accounts for the difficulty in movement and spasticity seen will ambulating. Some specimens at this stage are immobile until the the state of rigor mortis passes which take generally about 12 hours depending on the enviornment and ambient temperature.

    b. Bloat state: early physical state from the effects of enzymatic breakdown[autolysis] of proteins, lipids[fats] and carbohydrates resulting in the release of gases such as hydrogen sulfide, methane and carbon dioxide. Body fluids from natural liquids and liquifying tissues increase and due to increased pressure from gas formation create a process of “purge fluid release” forcing the liquids from natural orifices such as the mouth, nose, rectum. This stage of Zombotic existence is the most horrific and malodorous as a result of the formation of the toxic amines,known as “cadaverine” and “putrecine”. These amines are toxic at high levels. The overall appearance is one of extreme distention and dicoloration seen in Zombotic specimens at this stage their life cycle. Activity is moderate.

    c. Active decay: This stage in the Zombotic life cycle results in the largest loss on tissue mass as a result of the voracious feeding of maggots and the massive fluid purge occuring. It is not uncommon to find large accumulations of purge fluids surrounding the specimen at this stage and this in known as a “Zombotic fluid island”. Also large areas of skin “blisters” form containing putrefied tissue liquids. Zombotic specimens are most active in this stage of their life cycle. This stage can exit for long periods of time. The end of the active decay stage is noted by the migration away of the maggot population.

    d. Advance decay: Decompostion is now rapidly decreased as a result of the loss of readily available cadaveric material. This stage of the life cycle is the most protracted stage in the Zombotic life cycle. Zombotic specimens in these phase of the life cycle active however much less so than during the acive decay stage. Tend to be slow moving as well.

    2. pH
    Due to the loss of tissue oxygen and the increase in carbon dioxide in zombotic tissue, the pH is found to be acidic at pH values of 1 to 1.5

    3. Body temperature
    The core temperature is found be 35C or 95F.

    4.Odor: Cadaverine and putrecine give zombotic specimens their classic oderant red flag.

  2. I am very intrigued about a fungal basis for zombie reanimation and relatively slow rate of decay. I think this may explain also why there seems to be a total lack of blood circulation according to some authorities. Fungal structures would obviate the need for the normal animal blood vessels and cirulatory system to pass nutrients, gases, and other elements around the organism.

  3. Perhaps the microorganism causing a zombie’s reanimation is not a virus but a fungus. Fungi can get energy from decaying matter, and many of them are also bactericide, vermicide, etcetera. So, maybe a zombie is just a fungus that uses a human corpse as a vehicle to move around and extend its DNA in a faster way. It somehow stimulates the hunger in the zombie’s brain in order to get itself a source of decaying meat from which to extract energy. So, if the zombie does eat, the fungus feeds on the content of his/her stomach; if the zombie does not, then the fungus has to feed on the zombie’s rotting body itself. While, scavengers like insects, other fungi and bacteria are repelled by the z-fungus.

  4. Then again we could have walking wasp nests if you think about it since the zombie is not fpdeterred by pain.

  5. Mario Limbouris

    I think insects will be a big factor.It’s possible that a Zombie would actually STOP moving if there’s nobody around.A Fly could then land on it and lay its eggs.When the eggs hatch,Maggots will emerge.Maggots eat dead flesh which is basically what a Zombie IS.So,the Zombie would become significantly weaker and may even have trouble moving after a while.

    • That gave me an idea, why not plague the zombies instead, just idk, throw fly eggs at the zombie or something. Why not make phosgene oxime, I’m pretty sure that’s considered a corrosive gas.

  6. Would like to add the following on the “movement” part, i live in Panama, here you have lot’s of insects that dont give a damm if the animal is moving to put it’s larvae, we have lot’s of problems with certain fly’s that put their eggs on the point if the ears of the dogs, (a sensitive and quick movile part of the dog) and yes, the dog even shake it’s head , move the ear and even use it’s legs like scratching, the insect just hover 3 o 4 cm’s away and then come back, same with cows and other animals, so, a slow minded zombie should be piece of cake for this insects, there are others that just need to bite you to inject its eggs and then you have this horrible flesh eater worm inside you (here caled “torsalo”) of course this things wont happen on the city thanks god but in rural areas this things may feast on a living corpse easily as they do with a full aware human. Just a thought, there are insects and there are insects 🙂 regards.

    • Javier, you make a good point and aggressive flies would certainly be the least deterred. I still think movement is a potential mitigating factor, especially when we take into account that a large number of necrophagous insects are beetles that rely on their meal staying put. They simple lack the mobility to chase and feed on a moving corpse.

  7. My worry is whether or not these same insects can receive the infection, and if THEY can spread it to other humans.

    • Tasker, that’s a whole different discussion. The insects that feed on carrion are not usually the ones that spread a disease. It’s the ones that feed on living creatures: ticks, mosquitoes, fleas, etc. If they feed, or even try to feed, on a zombie, it could be all bets off.

  8. 1) Climate 2) insect activity 3) how fast I kill them

  9. it’s also possible the biochemical process involved in the reanimation may alter the rate of decay as well. actually, i might even be necessary to enable enough brain function for the zombie to reanimate at all. any decomposition of the areas of the brain a zombie would need for sensory perception and motor functions would have to decay slower than the rest of the body simply to keep them going. most damage visible to zombies has been from external effects such as weatherization/eroding and physical injuries

  10. I think before decomposition rate can be judged, one must understand the cause of reanimation. If decomposition proceeds normally, the threat would dwindle in the first couple years for most environments. Once the musculature, ligaments, and tendons have degraded enough, the zombie would cease to be a threat. In the case of a biochemical cause, the bodies may be tainted in such a way that normal parasites/scavengers will avoid them which would might simply leave them to a normal decomposition rate. Of course, some biochemical agent able to cause reanimation may also retard the normal decomposition rate in which case the zombie could remain a threat for a much longer unanticipated amount of time.
    As EricR postulated, there could also be a correlation between feeding and decomposition or even reconstitution. If there is enough brain function left to keep a corpse walking and hunting, there may also be enough function remaining for the body to try and heal, after a fashion. If the reanimation is viral, bacteriological, or parasitical in nature, the causal factor may be able to convert flesh and blood to base components to help maintain the infected body… this may not require a complete digestive system as we know it. By the same token, this sort of cause may actually render the zombie combat ineffective in less time if food/fuel sources are not readily available and the disease starts to consume the zombie’s own body.
    If, as some writers have suggested, the zombies are caused by supernatural means, normal factors are immediately tossed out the window. Likewise, for the science fiction generated zombies generated by some space-born factor, it is also a complete toss-up on whether or not normal physiological reactions could be expected.
    In the end, I think the best case scenario is that the worst of the zombie apocalypse would burn out in about two years and dwindling to virtually no threat within 10 years (without scavengers/insects) simply due to normal decomposition aided by environmental exposure.

  11. Michelle McDonald

    The weather would contribute to many factors. Decay, lifespan of insects and how long the instects live. If a zombie is in freezing conditions they would last longer due to cold tempatures would slow the decay and insect activity. In a rainforest enviroment, zombies would not last long, the combination of heat and moisture would excellerate the insect activity

  12. I’ve theorized the possibility that the feeding process might act as a way in which a zombie might slow its decomposition. Thoughts?

    • 1Lt. Chris Post

      I see where you’re going and this will actually be discussed in part 2 of this series. My short answer for now is yes, the feeding process could slow decay.

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