Season 1: Episode 2- The Ents (Lord of the Rings- 2002/2003)

This week we look at the Ents, of the little known cult comedy Lord of the Rings. Adam really just nerds the fuck out (we get it you read), Dave reveals he doesn’t believe in new Zealand and Sam rediscovers the art of the pun.

Movie History – 0.04.55
Movie Any Good? – 0.16.38
Ent Physiology – 0.21.06
Ent Ecology – 1.01.02
Treebeard vs. Christopher Lee- 1.24.30

Film: Lord Of The Rings- Two Towers [2002]
Production Company: WingNut Films & The Saul Zaentz Company
Distributed By: New Line Cinema
Monster: The Ents
Featuring: Sam, Adam, David
Rating: Mature (for some offensive language and adult themes)

Episode 2- The Ents Fact Sheet



Ents- Physiology
New Line Cinema, 2002


Tolkien’s Ents pose a lot of difficult questions regarding how they would function in the real world. How would they walk? What would they be composed of? What would they eat? Some of these questions we tried to answer in the discussion below.


In the film, Treebeard appears as a 14 foot moving mass of leaves and branches. In order to discuss if a walking tree could exist, we need to look at some of the examples of plants that move on Earth.

Plants That Move
In nature, there are examples of fast moving plants. Despite what some legends might lead you to believe, there is no such thing as walking plants. The walking palm tree (Socratea exorrhiza) doesn’t actually walk and although the roots look like small legs, the plants are rooted in the ground like other forms of vegetation.

There are examples of fast moving plants in nature. For example, the venus flytrap closes in approximately 100 milliseconds using an electrochemical reaction triggered by an insect walking through its trap. However, the mechanism requires a long time to ‘recharge’ and cannot be repeated over and over, like would be required for walking. Other examples of fast movement in plants range from spor propulsion in the Sphagnum mosses, to leaves that fold at night in the Mimosa pudica, to the fast moving tendrils of Bryonia diocia. All of these plants employ mechanisms that rely on rapid changes in electrochemical gradients or hydrostatic pressure. They cannot be repeated at a pace that would allow for an Ent to walk.

Animals With Plant Symbiotes
A more realistic mechanism of how an Ent might work in the real world, would be a type of mammal that employ a symbiotic relationship with plant species. The best example of this in nature is sloths [Suutari 2010]. Sloths are slow moving mammals, moving around two metres per minutes and sleeping for up to 20 hours per day in trees. Their slow movements and arboreal lifestyle allows for the growth of algae within their fur. The algae species are transferred from mother to offspring, are rather unique to sloths (Trichophilus welckeri), and offer advantages for both species.

Final Thoughts- Ent Design
If the Ents were to exist in nature, the best basis for them to work would be as a mammal with a symbiotic plant or variety of plant species growing on them. I propose that an Ent would be type of primate standing erect at approximately 14 feet tall and with multiple plant species growing on its’ skin.


Like in our previous discussions, our Ent mass will need to apply by the square-cube law as the size increases. As we are basing our Ent off a large primate we can simply scale up a human to get an approximate idea of how it could work:

  • Average Human Adult Male Height= 1.78 m
    Average Human Adult Male Weight= 79.4 kg)
    Ent Height= 4.2 metres [2.36 times taller than human]
    Ent-Mammalian Component Estimated Weight= (79.4)(2.36^3) = ~1043 kg

Final Thoughts- Mammalian Mass
The mammalian component of the Ent would weigh around 1000 kg. Most likely the weight would also increase with the addition of the symbiotic mammalian component growing on him.  


The Ent would have a metabolic rate that scales with Kleiber’s law like previously discussed with King Kong. Based on their actions in the film we believe that they would live primarily sedentary lifestyles and would spend most of their time in a state of reduced activity. They would likely have a metabolic rate similar to other slow moving mammals like a sloth.

  • Sloth mean basal metabolic rate= 145 kcal/day [Pauli 2016]
    Sloth mean weight= 4.3 kg
    BMR = (a)M^¾
    *Solve for (a)
    145 kcal/day= (a)(4.3^¾)
    a= 49Estimated Ent Metabolic Rate: (49)(1043^¾)=  8993 kcal/day

To calculate the estimated Ent DER, we need to decide how active we feel that they would be. Based on what we see in the film, I am comfortable saying that the Ent’s metabolic rate would be between 1 and 1.2 times his BMR.

  • Activity factor= 1-1.2 x BMR
    DER= 8993-10,792 kcal/day
    DER (mean)= ~10,000 kcal/day

Final Thoughts- Metabolic Rate
The Ents would have daily energy requirements around 10,000 kcal/day. Although large, this number is comparable to other large mammals and could be met using similar mechanisms for hunting and foraging. However, hey would not be able to survive off only Ent Draught alone as discussed in the film.


In order for the plants to survive on our Ent, they will need to have their own mechanisms for gathering nutrients. Although they will be able to obtain a steady supply of carbon dioxide and sunlight from their surroundings, by being attached to a moving mammal they will miss out on the nutrients that they traditionally get from the soil. They may be able to meet their fluid requirements using the sweat produced by the Ent, but will still need to gain phosphates, nitrates, and other essentials from another source.

Final Thoughts- Metabolic Plant Component
I propose that the plants on the Ent could meet their nutrients needs through two mechanisms. The first would be through temporarily rooting during the periods that the Ent is inactive, to allow them so form of soil nutrient absorption. The second would be to create a varying flora that grows across the Ent with multiple species contributing to the help met the nutritional needs. This would include vines with modifications similar to what is seen in the venus flytrap, to allow for the breakdown of insects to meet needs traditionally covered by the soil. At 4.2 metres in height, the Ent will have a total surface area of around 10.6 m^2. This is a lot of space for different plants to grow.


The Ents would have requirements similar to those seen in other animals. However, in order to try and supply fluids to the plant species attached they would also need to produce enough fluids for absorption on their skin.

  • Mammalian Metabolic Fluid Requirements
    Fluid Maintenance Rate= 50-70mL/kg/24hrs
    Ent Mass= 1043 kg
    Fluid Maintenance Rate= (60)(1043) = 62,580 mL/day
    ~63 L/day
  • Mammalian Sweat Capabilities
    An average person loses ~600 ml per day, but you can lose >14 L/day [Bates 2008]
    Ent is 2.36 times taller and has 5.57 times more surface area than a average human
    An Ent could lose up to 5 times more sweat than a human, or 72.5 litres/day
  • Plant Fluid Requirements
    Estimated Ent Surface Area= 10.6 m^2 or 114 feet squared
    Water needed for plant coverage= 6.40 gallons / day or 24 litres / day
  • Total Fluid Requirements
    Ent Mammalian Needs + Plant= 63 L + 24 L= 87 L/day

Final Thoughts- Ent Fluid Requirements
In order for the Ent to meet the fluid requirements of the symbiotic plant component, they would need to consume at least 87 litres per day. As a comparison, the average human requires approximately 3.7 litres per day. Although this fluid requirements are high, they could be met. Throughout the film the Ents are seeing drinking large amounts of Ent draught and this needs could be met within their surroundings.


The Ents would not be able to bind the symbiotic plant species to them directly. Penetrating roots would create open wounds and wreak havoc on the underlying immune system, musculoskeletal system, and vasculature. Instead, it would make more sense to have the plants winding over the skin/integumentary system and sharing any nutritional needs through the skin (transdermally). This would require the ent to have a layer of hair on the mammalian component that would allow for fungus and vines to grip. The skin would not be able to be extremely thick or it would interfere with sweating and the transmission of water.


Like we discussed with Kong, the Ents will have limitations imposed on them by their size. Because of their weight they will be slower moving, will not able to jump, and will be able to life less than 50% of their body weight. Unlike what is seen in the films, the Ents would not be able to throw large boulders or smash down dams. Furthermore, they will be even more restricted by the weight of their plant symbiotic component. We can calculate approximately how much the plans on our ent would weigh:

  • Average vine weight= 0.3 lb/foot or 0.44 kg/m
    Average Ent Coverage= 10.6 m^2
    Assume Treebeard’s Plant Coverage is 1 Inch ThickMulched barck at 1 inch thick covers 24 square feet and weighs 20 pounds
    *This means that the weight per m^2 will be approximately 3.9 kg (3.9 kg/m^2)
    Plant Weight= 41.34 kg or 100 pounds of dry weightOne litre of water has a mass of almost exactly one kilogram
    Average water use by the plant is at least 24 litres= 24 kg of weight*Total Mass (Dry Plant + Water)= ~70 kg

Final Thoughts- Skeletal/Musculature
The Ents would be tall, slow moving, creatures without super strength. They would be carrying approximately 70 kg of plant material on them at all times. In order to allow for movement, the plants bound to their skin would need to remain flexible and elastic.


As a mammal, the Ent would be able to breathe like most other terrestrial life. Contrary to popular belief, the presence of plants on the Ent would not enhance their ability to breathe. Although the plant mass will be producing oxygen it will not improve the ents respiratory capabilities significantly.

  • Ent Mammal Respiratory Component
    Ent Respiratory Rate (breaths/minute) = (53.5)(1043^-0.26)= 8.78 breaths/min
    1 liter O2= 4.8 kCal [Schmidt-Nielson 1997] or 0.208 litres of O2 : 1 kCal
    Ent DER= 10,867 kcal/day
    Ent O2 consumption per day= (10,867)(0.208) = 2260 litres of O2/day
    ~3.23 kg of O2/day
  • Ent Plant Oxygen Production
    Average Plant O2 Output= 150 grams of plant tissue : 32 grams of oxygen/day
    *1 gram plant produces 0.2 grams of oxygen
    Ent Plant Weight= 70 kg
    Estimated Plant O2 Production= (70)(0.2)= 14 kg of Oxygen/day

Final Thoughts- Respiratory
The Ents will be breathing just like other mammals and should have no difficulty meeting their O2 demands. Furthermore, the plant mass they are carrying should be contributing to the overall oxygen of their surroundings. However, the primary issue that they will experience will be associated with is compliance, or flexibility of their respiratory structures. Due to the presence of plant material on their chest, it is feasible to assume that as the vines continue to grow and eventually lose elasticity, that breathing will become more difficult. This might have long term implications for the Ents.


The Ents cardiovascular system will not be that different than what is seen in other large mammals. I used equations from a paper previously discussed in the Kong discussion to determine that

  • Ents Blood Volume
    Blood volume (mL)=(65.6)(1043^0.995)
    Blood Volume (mL)= 66,084 mL
    ~66 L
  • Ent Heart Rate
    Heart rate (beats minute−1)= (241)(1043^-0.25)
    Heart rate= 42 bpm


In order for the Ents to survive with a large plant burden directly attached to their skin, they will need to have an incredible immune system. The plants will hold water to the skin and carry bacteria on the roots, making an ideal environment for secondary skin infections. It may also be beneficial to have some forms of fungi as part of the normal flora that will be producing antibiotic compounds onto the skin like beta-lactams (the root of penicillin).


In the movies, we the Ents are thousands of years old. An improved an immune system will potentially help them to achieve an increased lifespan but it would only be one part. They would also need changes like increases to their telomeres, the presence of telomerase, and a diet rich in compounds to help with defence against genetic mutation and free radical buildup associated with age.

One of the theories behind what would eventually lead to the demise of the Ents would be the growing plant mass on them. As the plants continue to grow and eventually start to restrict the Ent’s movement more and more, the Ent will become more sedentary. Longer periods of inactivity will eventually allow the temporary roots to become more permanent and could eventually hold the Ent in place. The trapped Ent will eventually perish and the rest of the Ents that so rarely see death will begin to form their own view regarding Ents turning into trees when they grow depressed.


Ents- Ecology
New Line Cinema, 2002



As far as the biological and evolutionary history of the ents goes, we don’t get much from the movies (though the books have plenty to say). For the purposes of defining these organisms within the world of Middle-Earth we will use parallels between the ents and organisms that we have on Earth to try and work out how they could have evolved to the form that we see in The Lord of the Rings.


In the books, the history of the ents is given in excruciating detail. Basically, they were made as-is somewhere between 5,000 and 65,000 years ago. Since we need to define these organisms in evolutionary space, we are going to say that they started out as large endothermic mammals, likely primates, and at one time some members of the species developed a mutualistic and beneficial relationship with various plant species. This could have happened if some plants started growing in the fur of these rather slow-moving organisms, acting as camouflage and protecting the young ents during a time when they could be vulnerable to predators. As a result, the ents that had this relationship with the plants survived at a higher rate than those without it, and the trait became fixed in the population.

The cool thing about this adaptation and mutualism with the plants is that it will convey a habitat-specific advantage. That is to say, the ents will have plants growing on them that are native to the habitat that they live in. This is a double-edged sword, as they will be protected in their native forests but will possibly stand out if they tried to expand their range and live somewhere else.


Like all mammals, the ents are going to reproduce sexually. We are told in the movies that there used to be entwives, but that the ents “lost” them. What actually happened is that most of the entwives lived in a different habitat, on the other side of the river next to Fangorn Forest. During one of the great wars that took place before the movies that entire area was obliterated, likely killing all of the entiwives. As a result of this, the ents cannot reproduce to make more “entings”, or young ents.

Because the ents can no longer reproduce, they are what is called a “walking dead” species. This is a species that, for one reason or another, is going extinct and there is nothing that can be done. This can be the result of a changing environment, disease, or invasive species outcompeting the native species. With the ents, it is because only male ents are left and they cannot produce another generation. When the last ent dies, the species will be extinct.


We previously defined the relationship between the plants and ents as a mutualistic one, where both species gain a benefit from the other. The interesting thing about mutualisms in nature is that they are not stable in the long run and are vulnerable to “cheaters”, or species that find a way to gain a benefit from the other without providing anything themselves. The only way that these relationships can be maintained is if the members have a way of punishing cheaters, like an ent that could remove plants that don’t give him any nutrients.

If a species does find a way to cheat,or if one species costs its partner more than it gives,  the relationship switches from mutualism to parasitism. This is what is likely leading to the deaths of the ents, where the plants take more and more nutrients from the ent, constricting the movement more and more, eventually leading to a slow death strangled by the plants that used to be so crucial to their survival. We see this reflected in the literature, which indicates that ents “turn into trees” when they become sad, however this is likely just the ent dying and the plant-life taking over.


The ents are likely going to need to consume some kind of meat proteins to survive, though probably not too often. There are two possible ways that this could happen: symbiosis with carnivorous plants, or ambush predation.

There are many carnivorous plants in nature, and they entice other organisms with the smell of sweet nectar, fooling their prey into thinking they are about to have a tasty treat, when in reality they are becoming the treat. If some of the plants on the ent are carnivorous and consume insect, small rodents, or even birds, then it is possible that the ents are receiving some protein from the plants.

What is far more likely, however, is that the ents are ambush predators. The are covered in natural camouflage and remain stationary for extended periods of time, like an alligator or praying mantis. And much like those ambush predators, prey animals would not be aware of the peril they are in until it is too late. This can be seen in The Two Towers, where Pippin climbs up Treebeard THINKING HE IS A TREE. Pippin should be thankful that Treebeard was more worried about smashing the orc than he was having a nice hobbit-sized snack.


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Behie, Scott W., and Michael J. Bidochka. “Insects as a Nitrogen Source for Plants .” Insects 4.3 (2013): 413–424. PMC. Web. 24 Aug. 2018.

Scorza, Livia Camilla Trevisan, and Marcelo Carnier Dornelas. “Plants on the Move:  Towards Common Mechanisms Governing Mechanically-Induced Plant Movements.” Plant Signaling & Behavior 6.12 (2011): 1979–1986. PMC. Web. 28 Aug. 2018.

Bates, Graham P, and Veronica S Miller. “Sweat Rate and Sodium Loss during Work in the Heat.” Journal of Occupational Medicine and Toxicology (2008): 4. PMC. Web. 28 Aug. 2018.

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