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I have an idea for an encounter in my world that goes like this...

A weary group of adventurers are trekking through a great ancient forest. This forest is avoided by most due to strange tales of the forest attacking travelers.

Undeterred, the stalwart group of heroes delves into the foreboding wilderness to reach their goal; an ancient city long thought lost or even a myth. As the days pass, the trails disappear and the forest is clogged with dense underbrush and the trunks of trees are wrapped in vines and ivy.

As they press through the mass of green, they begin to notice thorns from some of the larger vines puncturing their skin and as they begin to realize just how tangled they are, the vines begin to constrict...

Design requirements:

  • Must rely on other plants (namely trees, though it could work on rocks too) for rigidity
  • Have thorns, the thorns should be able to siphon bodily fluids (namely blood) as a nutrient source, think of it as a viney mosquito
  • Be able to contract. It does not need to be aware and intentionally constrict, but should begin to constrict in some manner when creatures get tangled.
  • Mutual symbiosis. I want this creature/plant to be parasitic to trees, but I also want the presence of the vines to be a net benefit to the trees. There may be time between creature feedings so the vines will need the stability a tree offers...plus I don't want all the trees to be dead.
  • Will not be rooted to the ground but rather the tree.
  • Can grow up to 30 feet long and up to six inches wide at the base

Things to consider in an answer:

  • How do the thorns work, what mechanism allows them to extract fluids
  • How do the vines constrict, if they can also lift a creature that would be a bonus
  • How does the vine contribute to the well being of the host? (I want it to be a mutually beneficial arrangement) Keep in mind the size of the vine, let me know if the value to the tree likely ever becomes a detriment to the tree.
  • What type of creature in the real world most resembles what I have described?
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    $\begingroup$ Sounds like something from the Bonegrass Savannah. I approve. You’ve got an awful lot of questions in one question though. You should probably split those into multiple linked questions to get better, more specific answers. $\endgroup$ – Joe Bloggs Feb 14 at 19:40
  • $\begingroup$ @JoeBloggs I'd argue that they have to function together so getting the different aspects of the creature in separate questions would end up with answers that don't work together. $\endgroup$ – James Feb 14 at 20:35
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    $\begingroup$ The method of constriction and the method by which the thorns extract liquids certainly don’t have to be combined, and there are two very seperate answers for each of those questions for ‘which creature works the most like this’, surely: otherwise a blood sucking constrictor vine would be the only reasonable answer to your last question... $\endgroup$ – Joe Bloggs Feb 14 at 21:24
  • $\begingroup$ I don't have time for a full answer (meh work) but how about the vines only need one element of the blood, say the iron within it and passes the rest of the nutrients to the tree. Using iron would also allow for a the vines to have blood red leaves to go with the name.. Do like the possibilites of this $\endgroup$ – Gawainuk Mar 6 at 18:00
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Your vines constrict in the same way Mimosa (sensitive plant) leaves contract - an action potential triggering water movement within the plant.

. https://en.wikipedia.org/wiki/Mimosa_pudica

These types of movements have been termed seismonastic movements. This reflex may have evolved as a defense mechanism to disincentivize predators, or alternatively to shade the plant in order to reduce water lossage due to evaporation. The main structure mechanistically responsible for the drooping of the leaves is the pulvinus. The stimulus is transmitted as an action potential from a stimulated leaflet, to the leaflet's swollen base (pulvinus).... The pulvini cells gain and lose turgor due to water moving in and out of these cells, and multiple ion concentrations play a role in the manipulation of water movement.

When the vines feel they are being moved, they move water within themselves in such a way as to tighten and curl up. This deters predation by preventing a more uniformly thorny surface and that was its original function. Sometimes animals would be caught within the vines because of this action, which led to the additional functions.


Struggling creatures can damage vines. The thorns have a toxin which slows struggling and causes creatures within the vines to be passive.


Sleepy, torpid creatures caught within the vines tend to die - of thirst, if nothing else. Sometimes predators come and take them. Sometimes the predators are themselves caught. A dead creature caught in the vines tends to stay, at least in part, within the vines.


Thorns absorb nutrients the same way plants absorb nutrients anywhere - via roots, here adventitious roots. The roots are put forth into the dead matter captured within the vines, and ramify within the corpses, filling the space. This has to happen fast because the plant wants the resources of the corpse, and it is in competition with fungi and insect decomposers. At some time later the root shape of a corpse may be the only remaining trace of it.


These vines grow in nutrient poor areas. They do not photosynthesize. Your model is the parasitic plant dodder.

dodder

http://www.indefenseofplants.com/blog/2015/9/30/a-dose-of-dodder

Dodder begin their lives just like any other plants. Seeds in the soil germinate under a certain set of conditions and begin their trek into the sunlight. However, unlike many other plants who spend a lot of their initial energy setting up root systems, dodder only sends out meager baby roots. It says "forget that" and starts searching for a victim. It whips about in a circular motion like a cowboy's lasso. It is looking for the nearest host.

So too your plant (which looks just like dodder, with thorns). It is nonphotosynthetic. It grows on trees and shrubs and whatever it can find. Plants provide plenty of carbohydrates but are poor sources of nitrogen and other nutrients compared to animals and really it uses the tree as a sound anchor, so when the vine scores a big catch it has the leverage to keep it in place. The tree likes this too, because when the vine scores big a lot of the nutrients wind up washing down to and into the ground either from the corpse or from shed vine bits. The tree gets all of those.

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Your vines could act like a modified Sundew Plant, Drosera. Long vines hang down from your tree, they grow a form of delicious fruit; your victim pluck a fruit brushing the vine in the process.

Small trigger-hair send a signal to the vine, through Thigmonasty the vines constrict around the victims limb; long hooked thorns hooking into its skin. Your victim thrashes, further entangling the victim in its vines, more thorns hook in painfully. The vines swell as fluid is pumped into them, constricting the victim, pushing the thorns further into the body.

But that's not what kills the victim, no, intense pain shoots through its body as the vine pumps a mixture of enzymes (Sundews use Esterase, peroxidase, phosphatase, and Protease) through its thorns, into its bloodstream, beginning to digest the victim from the inside out. The victims nutrient soup begins to drip onto the vines and ground around the tree, giving them both vital nourishment.

The victims decomposed corpse drops to the ground, what's left is eaten by scavengers and is further absorbed into the ground. The scavengers also eat through fruit, its seed deposited through the forest in the scavengers scat.

The forest becomes calm, the vines relax, luring its next victim with its delectable fruit, it has become stronger, larger, its host healthier and taller. Nothing remains but a soupy stain on the forest floor.

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  • $\begingroup$ You manged to spell out most of what I was thinking when I was reading the question. Since the OP was kind of wanting to use the Thorns themselves to extract fluids, I was thinking of the combination of Enzyme to digest and a hollow thorn with fibrous interior to use capillary action to siphon nutrients directly. Great answer! $\endgroup$ – Paul TIKI Mar 6 at 15:38
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Have a look at the Wait-a-while plant (There are actually several plants with this name).They actually grow like a bush, but you can easily change the appearance to vine-like.

enter image description here

These plants trap animals with their thorns that entangle in the fur and skin. Humans are intelligent enough to stop for a second and move in the opposite direction to untangle themselves (hence the name wait-a-while), but animals panic. The more the animal struggles to free itself, the more it gets entangled, eventually dying of thirst.

Due to the bush-like growth of the real-life wait-a-while, the dead animal now lies within range of the roots. The slowly rotting cadaver fertilizes the plant.

Your Assassin Vines need to reliably catch and kill their victims and then extract nutrients from them.

The catching is done with tiny but sturdy thornes bent towards the vine to best entangle fur. To kill the prey, it's better to use poison (like nettles or jelly fish) than to move the vine around. The panicked, thrashing victims do enough of their own moving around to entangle themselves effectively.

To extract nutrients, the Assassin Vines could grow tiny air roots from buds located under every thorn. The pull on a thorn activates the buds and tiny roots start growing towards the victim. Those roots that "find" the body enter it through wounds, spread inside the cadaver and grow thicker and stronger to extract as much nutrients as possible.

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