Jellyfish are... weird. They're clear, slimy, and can sting after death. Sounds perfect for experimentation, so lets weaponize them!

Consider a hypothetical world where jellyfish are extremely common and you can get them cheaply anywhere, and there's an extreme fascination amongst the human population with them. In this world, there's a war going on but there's a shortage of materials. Luckily, you have millions and millions of Jellyfish at your disposal, stocked up. (Don't ask why the government has them stored up)!

The government has asked you to design some weapons using those jellyfish as parts.

You can use any part of any type of jellyfish in your weapon, but the main application of the weapon must be based off of jellyfish.

Main list of weapons types:

  • Projectile weapons
  • fluid weapons (flail, whips, chains)
  • rigid weapons (Swords, clubs, staffs)
  • Armor/shielding

Of the above types, how effective would the jellyfish based application be, how would it work/be made, and how well would it work (against traditional weaponry (modern) and other jellyfish weaponry)?

Note: Bonus points for coming up with a jellyfish based war machine!

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio Jun 4 '15 at 2:38
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    $\begingroup$ All I can think of is this: vignette1.wikia.nocookie.net/despicableme/images/d/d6/… Know it's not jellyfish :D $\endgroup$ – xan Jun 5 '15 at 10:15
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    $\begingroup$ "Don't ask why the government has them stored up!" - That's easy - they're a delicacy in the world you're creating. $\endgroup$ – Andrew Grimm Jun 6 '15 at 2:26
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    $\begingroup$ We already live in such a world $\endgroup$ – Tom J Nowell Jun 6 '15 at 14:12

11 Answers 11


Would you be interested to know that annually, Jellyfish kill more than ten times as many people as sharks do? Not bad for a creature that is 95% water and doesn't have a brain!

That being said, aside from stinging people to death and weighing down fishing nets, jelly fish are pretty slow and useless (6m/min is considered fast for a Jelly fish). They wouldn't be any good for delivering projectile weapons, attacking with melee weapons, and there'd be no point in armouring them.

Jellyfish could be weaponized, just not in any of the ways you've proposed, except maybe with a whip, which wouldn't actually whip people, but just touching them would be sufficient to kill them, in fact this is how 20-40 people die in the Philippines every year, by coming into contact with one of the 3m long tentacles of the box jellyfish.

Jellyfishes Greatest Advantages

  1. Numbers: There are literally BILLIONS of jellyfish in the Ocean, and they mass in swarms of thousands and millions. They only live for a few months, so their numbers constantly grow and regrow, you can kill as many as you want, and in only a few short weeks or months their numbers can be back to what they were. In 2005 a Swedish Nuclear plant had to shut down because of a jellyfish invasion, the sheer numbers clogged the cooling system, threatening a meltdown.

  2. Stealth: Jelly fish are 95% water, so it's hard to distinguish them from the rest of the ocean water, there are even some species that appear to be completely invisible to the naked eye while in the water. Though slow moving, a massive swarm could approach a target without being easily detected by instruments.

  3. Fearlessness: Jellyfish have no brains, they only have a simple nervous system, this makes them mindless and fearless, they are essentially the zombie hoard of the ocean, innumerable, and unstoppable, combined with their sheer number, you could send swarm after swarm at an enemy.

Possible Weaponized Applications:

Since Jellies don't have brains, you can't really train them to do anything, and they're slow, so they can't chase anything down, or fight, or do anything really except for float around, but you could still make use of them.

  1. Sting Nets: Imagine an impenetrable net of Box jellyfish tentacles, anyone that ventures in gets stung and dies.

  2. Bombs: A jellyfish swarm could carry a huge payload of explosives, especially if they were modified so that a good percentage of their liquid mass was an explosive similar to nitro-glycerin. Such a swarm could make short work of ships, submarines, docks, even power plants and factories. They'd also work well as a defensive tool, no one's going to venture into a swarm of exploding jellies.

  3. Chemical Weapon Delivery: Jellyfish are known to wash up on beaches numbered in the millions and then just rot. Suppose they were infected with disease or an agent that turned into a toxic gas once exposed to the air and sunlight. The Jellies wash up on shore, and then their rotting corpses release whatever toxin they're carrying into the air which kills everyone within a mile of the beach, allowing an invading force to land on the beach unchallenged, and onto a softened battle field.

Essentially, you're going to have to work with the way Jellyfish currently behave, and think up applications which take advantage of their short lifespans, their mostly water body composition, and their sheer numbers in swarms. Mounting anything to a Jellyfish would be pointless, you may as well as try to attach a bayonet to a water balloon. You don't want to put anything expensive on a jelly fish either, because it's going to die in less than 6 months anyways, and you can't train them to do anything, because they won't live long enough to learn anything. You'd have to develop a signal or something you could use to control the swarm and where it goes, take advantage of their numbers to overwhelm an enemy and choke them out.

Read these fun facts about jelly fish.

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    $\begingroup$ I'm going to +1 this because even though it seems like you may have misunderstood the question, you still managed to make a very valid answer (eg: the net and swapping out the liquid mass for explosives - jellyfish grenades, anyone?). For clarification though, I didn't mean to ask how to weaponize live jellyfish. I meant to ask about how to use jellyfish parts in weapons, but it's my fault for being unclear. I won't change the question though, since this answer is really good and I don't want to invalidate it. $\endgroup$ – Aify Jun 2 '15 at 19:25
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    $\begingroup$ @Aify Then the obvious answer is in their toxins, Jellyfish are the most venomous creatures on earth, using their venom to poison people would be the most obvious answer. Aside from that, there's not much more to their anatomy that would be useful, as I pointed out, they're 95% water, and have no solid parts. They are literally a gelatinous mass, not really good for anything except for eating (If you have the acquired taste for them). $\endgroup$ – ShemSeger Jun 2 '15 at 19:36
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    $\begingroup$ Jellyfish are unstoppable? Tell that to the ones lying on the beach. $\endgroup$ – David Richerby Jun 3 '15 at 12:29
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    $\begingroup$ 95% water and no brain? TIL I work with mostly jellyfish. $\endgroup$ – corsiKa Jun 3 '15 at 19:10
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    $\begingroup$ "Not bad for a creature that is 95% water and doesn't have a brain!". As opposed to some of the co-workers I've suffered with, who replaced water with hot air... :-) $\endgroup$ – Bob Jarvis Jun 4 '15 at 18:52

Now kids, don't try any of what you are about to read at home. You do not want to mess with the Geneva Convention.

I am going to answer both, how you can weaponize jellyfish (sea jellies, to be pedantic) and how to take what we've learned from jellies to make more powerful weapons.

First off, start your breeding program now. You are going to want lots of them. Get yourself a ton of the Malo kingi. Mess with the genes responsible for their breeding cycles. These guys are tiny and next to invisible in water. They weigh little enough that they have been picked up by waterspouts and dropped miles inland during a storm. They also have predictable migration patterns, and have been found to swarm toward bright sources of light.

Before you invade a country, seed the clouds in the area with silver nitrate, and when they build up to saturation, drop in millions of Malo kingi. Do not invade while it is still raining. You will regret it.

You may also want to add them to the drinking water about the same time. Drop them in an appropriate body of water and lead them where you want them to go with a small robotic swimming drone armed with a powerful laser.

The two steps above will decimate your enemy's population before you put a single pair of boots on the ground, maybe even leading to surrender.

Secondly, aside from the obvious poison, what makes jellies so dangerous is their hypodermic injectors. These are bundles of tightly wound filaments that uncoil to a thousand times their bound length and release with the slightest contact. Imagine a bullet filled with similarly coiled razor-wire. The moment it penetrates its victim, the core uncoils and rips the target to shreds.

Nearly any shot that penetrates a victim is a guaranteed kill, and if it collides with body armor, it will shred the fabric of it, disconnecting any plates. The second shot will hit a soft target. If these wound-roundsTM are coated with venom, the lacerations caused by a near-miss will still kill potentially multiple targets.

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    $\begingroup$ The drinking water poisoning suggestion just gave me horrible shivers to think about. I don't think the hypodermic injectors would really shred people or armor though, at worst they would just do exactly what they're designed to do which is deliver poison on contact with flesh. Good idea combining them with bullets though because that would make nearly any bullet wound lethal! $\endgroup$ – thanby Jun 4 '15 at 14:21
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    $\begingroup$ I love reading WorldBuilding, but sometimes, when I read answers like this one, I really hope it doesn't give ideas to some genius psychopath... $\endgroup$ – Gary Olsson Jun 4 '15 at 15:19
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    $\begingroup$ @thanby, I was just intending that we would take lessons learned from examining the jelly and apply it to weaponry. The filaments I put in the bullets would be razor wire made from the same memory-metal that modern glasses frames are. They prefer to be straight, and when the tension in the bullet is released, they get there anyway they can. I for one wouldn't want to stand in the way. $\endgroup$ – IchabodE Jun 4 '15 at 16:07
  • $\begingroup$ This answer makes me physically hurt in all the wrong places and for all the wrong reasons. $\endgroup$ – Friendlysociopath May 3 '18 at 4:35
  • Projectile weapons
    Jellyfish launched from a simple t-shirt launcher could be roughly equivalent to a taser in effectiveness (or worse if you can get a hold of a nice box jellyfish). Still, the range leaves something to be desired.

  • Fluid weapons (flail, whips, chains)
    Jellyfish jelly arms aren't all that great for tying together, but a flail with jellyfish heads would be fairly effective at adding pain to hits.

  • Rigid weapons (Swords, clubs, staffs)
    Jellyfish tentacles sting after death... perhaps applying grooves and lining them with tentacles? It would eventually run out of stinging ability.

  • Armor/shielding
    Removing the stinging parts of jellyfish leaves you with... jelly. It could be a pretty good filler for padding. It would weigh a lot (it's mostly water!) but you could probably line the walls of an attack truck with a layer of it fairly easily.

Jellyfish armor could protect you from blunt jellyfish weaponry (and the JellyLauncher (patent pending), but would prove ineffective against the stinging sword. Of the weapons, against a non-armored person the JellyLauncher would appear to be the weapon of choice. Even then, it wouldn't be as good as a modern weapon.

Ok, seriously: You could use the stinging cells in nearly any application, from dart guns to a plank with a nail in it, but most of these things are already deadly enough that the sting of your average jellyfish won't contribute much. This changes with box jellyfish, which can be deadly, but that still leaves you with low velocity weaponry or blunt weapons.

  • $\begingroup$ JellyLauncher pitch: Envision this, only with Jellyfish: youtube.com/watch?v=nYaGunazX5A $\endgroup$ – Slacklord the Terrible Jun 2 '15 at 17:58
  • $\begingroup$ Wouldn't jellyfish be too heavy for a t-shirt launcher? $\endgroup$ – Aify Jun 2 '15 at 18:01
  • $\begingroup$ @Aify Depends on the jellyfish. A 'portugese man-of-war' wouldn't be and would be very deadly. Im wondering if you could make a good whip out of a 'giant purple striped jellyfish', unfortunately I couldn't find one out of water,so I couldn't tell, what do you think? $\endgroup$ – Necessity Jun 2 '15 at 21:30
  • $\begingroup$ @AdamNicholls if we twist multiple tentacles together (kind of like rope), then a stinging whip would definitely be possible. Don't know how much damage it'll actually do though. $\endgroup$ – Aify Jun 2 '15 at 21:32
  • $\begingroup$ @Aify There are a few specimens that you could use there one large tentacle for but most would probably need twisting together. How much damage will any of these weapons do? It will probably do as much damage as an actual whip which is more than can be said by some of the ideas. $\endgroup$ – Necessity Jun 2 '15 at 21:51

The other answers pretty efficiently cover what you can do with stinging jellyfish. If I may summarize:

When dead: put on your enemies with whips/bombs/tshirt guns/long sticks. When alive: sic on your enemies, possibly fill with bang juice.

Now: let's consider nonstinging jellyfish for a moment. BUT WAIT you cry, what is the point of a stingless goop in warfare? Let me tell you about Pykrete. It's ice cut with fibers, which improves shatter resistance and raw strength, as well as melt resistance. Do you see where I'm going here? Gelatinous frozen-jelly-armor can be feet thick, shatterproof, and absorb thermal attacks. Because it's water-based, HEAT rounds will cause tiny steam explosions, neutralizing the shaped charge. Tanks coated with frozen jellyfish would have a jelly layer on the very outside roughly .5 jelly thick, anchored in a layer of ice. Deep inside the ice layer, put a condenser and cooling equipment to keep the ice cold over very long periods(for battle you can turn it off) and you can even repair your tank in the field with more jellyfish! Slop them on the craters in your armor, put a tarp over the thing, come back in the morning for fresh new impenetrable armor. (you said anywhere in the question. So. Anywhere.) In order to enhance thickness I would recommend putting iron rods through the armor like long spikes, to conduct heat down into the cooling zone and increase the thickness without having to get too overboard with chillers. Ice is a great insulator.

They're also probably useful as a glue when rendered down in a big vat, but not better than like, horse hooves.


When there is enough food and jelly fish they create very large swarms / blooms. These have been known to block up the intakes to power stations in the past. 1

Take a large number of jelly fish, plenty of jelly fish food and dump them in the sea near your enemy power stations. Inland power stations usually have a cooling lake near by.

Of course in your world you will need to seed the jelly fish inside the netting they would have to keep out the natural/local jelly population.

  • $\begingroup$ or just sabotage that net, and let the local population do what the net was there to prevent. $\endgroup$ – Matthew Najmon Jun 4 '15 at 19:22

Start with Irukandji jellyfish. These tiny creatures (the bell is roughly 5mm on a fully grown adult) are incredibly toxic. From Wikipedia:

Irukandji syndrome is produced by a small amount of venom and induces excruciating muscle cramps in the arms and legs, severe pain in the back and kidneys, a burning sensation of the skin and face, headaches, nausea, restlessness, sweating, vomiting, an increase in heart rate and blood pressure, and psychological phenomena such as the feeling of impending doom.

And all that is without any help from ill-meaning scientists. Oh, yeah, and by the way:

the Irukandji also has stingers on its bell


...the ability to fire stingers from the tips [of their tentacles] and inject venom.

And you thought Jaws was scary.

Now, if you have millions of these tiny creatures, there are a variety of ways you can weaponize all or part of them.

Water toys

The simplest way to weaponize them would simply be to fill a large-bore water gun with them and fire them at your enemies. Low-tech, low cost, and very dangerous, the tiny creatures will leave your enemies writhing in agony and doom at best. Body armor won't stop them, either; all it takes is a 5mm hole and the tiny jellyfish will sting them.

Any water toy will work, too. That's right. Squishy splash balls, sponges, water guns, water balloons, and even squirting rubber duckies could be converted into a weapon, simply by filling them with jellyfish. If you are a horrible, evil, black-hearted, soulless person, you could even send children with water guns to attack enemy soldiers. No one suspects a child with a squirt gun, at least until everyone starts screaming.


Dumping a few thousand live Irukandji in swimming pools, drinking water, even puddles on the side of the road will wreak havok. But why bother with the jellyfish? Extract the venom for use as a poison! There are countless applications for the venom alone; as an additive to anything from drinking water to improvised explosives, the venom can make a bad day much, much worse. victims won't be stumbling out of wreckage covered in dust; they'll be thrashing on the ground in burning agony. If you want to leave an impression on the local population, that's the way to do it.

Semi-Lethal Spreading Mines

A normal explosive mine is bad, but often it leaves nothing but a corpse, and if you're in a hurry, a corpse is easy to leave behind. Instead, fill mines with jellyfish barbs. Upon release, the barbs will be flung out to attach to anyone nearby, injecting them with the venom and leaving the victims in pain, but alive.

But that's not the worst part. When that soldier is taken to a field hospital, anyone that touches him without a strong pair of gloves (leather would work; thin rubber of latex would not) will also be injected with the venom, as the sharp, springy barbs stab into them. Even if all that happens is that contaminated clothing is washed with uncontaminated clothing, there is a chance for the barbs to spread.


Thus far, everything has merely used parts of a jellyfish. But what if we apply Science™? Breeding Irukandji jellyfish in captivity has thus far proven unsuccessful, but then again, we already have truckloads of the things, so I'll assume we've gotten that part down.

Once we can breed, we can selectively breed; as fast as jellyfish reproduce, it won't take long to create an even more powerful venom, or a venom that highlights certain aspects - for instance, the pain and agony part is reduced, while the "sense of impending doom" is strengthened. Now instead of a drug that causes pain, we have a mind-altering drug. Enemies gassed with an aerosol form would be panic-stricken, even to the point of self-harm.

Other non-lethal forms could include a sprayable form, similar to mace, or a diluted form use in riot guns or water cannons for riot control. It's hard to riot for the cause when you are shivering in pain and wallowing in thoughts of doooooom.

Note: Please don't try this at home. Or anywhere else. It's terrifying, and you'll probably end up stinging yourself (which is what the scientist who discovered the Irukandji syndrome did, though, and it got named after him; who knows, you might end up famous).

  • $\begingroup$ Are there many water toys with ~5mm caliber? I think ~0.5mm is more common. $\endgroup$ – Nicolas Raoul Jun 5 '15 at 2:38
  • $\begingroup$ The larger water guns usually have larger bores; I found a few searching for "water blaster". But, indeed, you would want to properly size your water guns. $\endgroup$ – ArmanX Jun 5 '15 at 2:55

Biggest problem you have is that you've been asked to do this by the government. So lets take care of that.

First, hire a bunch of pharmaceutical engineers. Have them develop an efficient way to extract poison from the jellyfish. Use that to supply the government with blow darts.

This will turn out to be lame, but since you're a campaign donor and since it's what the government asked for, just not what they needed, you'll be fine.

Now that you have a steady government contract you can hatch your real plan, skimming. Take the most deadly of the jellyfish out to make herbal supplements.

Don't actually claim it cures cancer and warn people about how incredibly dangerous it is. Make them sign liability waivers. The more you hype the danger the more people will want it anyway. Soon as someone dies dilute the heck out of it and call it "homeopathic".

Now you're free of reliance on the government.

Use this same cynical view of mankind to branch out into other ailments until you have a vast economic empire. Whenever your enemy's confront you, you can hire a team of lawyers to sue them into oblivion.

Or just smack em in the face with a bucket of jellyfish chum. Whichever's easier.

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    $\begingroup$ Made me laugh, but I still can't vote for it. $\endgroup$ – hildred Jun 3 '15 at 17:03
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    $\begingroup$ @hildred you don't think you could rule the world with a bucket of jellyfish chum and well paid lawyers? I've got a chum bucket with your name on it. And with all these lawyers I'm bound to get away with it too. But, maybe you're right. It needs something more. How about a social media blitz filled with claims that jellyfish pills will make you last longer in bed? $\endgroup$ – candied_orange Jun 3 '15 at 23:12
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    $\begingroup$ I Just can't vote for anything that gives lawyers more, well, anything but a facefull of jellyfish chum. $\endgroup$ – hildred Jun 3 '15 at 23:38
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    $\begingroup$ @hildred Brilliant! We'll produce a japanese style game show where contestants try to win a new car by throwing jellyfish chum at divorce attorneys. We'll call it Stingrays for Stingrays. It makes no sense but that's never stopped us before. $\endgroup$ – candied_orange Jun 4 '15 at 0:57

Never underestimate nature. Nematocysts can do some amazing things. Özbek et al. calculated accelerations of 5.4 million g in deployment of a Hydra nematocyst. Velocity was "only" 18.6 m/s but that was achieved in 700 ns. The tip hits the prey (armor piercing attack upon the shell of a crustacean) with 7.7 GPa pressure.

Özbek S; Balasubramanian PG; Holstein TW. 2009. Cnidocyst structure and the biomechanics of discharge. Toxicon. 54: 1038-1045.


All of these would be terrible, terrible choices. You're better off beating people with a tree branch than with a jellyfish, if only for the massive logistics issue. Just attempting to transport the jellyfish to a warzone will spoil them. You don't have the time to make weapons out of them unless you're doing it near the battlefield.

If the government gives you a large supply of stored jellyfish, the best way to weaponise it is to throw away the jellyfish and melt down whatever containers they were keeping it in. It probably contains more useful components than the jellyfish do.

As a final note: poisonous weapons are a really bad idea on a battlefield. The odds of brushing up against a friend and killing him, or touching the wrong part of your weapon are quite high. You are likely to suffer immense losses due to accidental poisoning of your own troops.

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    $\begingroup$ The question is, what kills better? A tree branch or a tree branch wrapped in box-jellyfish tentacles? I don't know about you, but I'd take the wrapped one over the normal one every time. $\endgroup$ – Aify Jun 2 '15 at 19:27
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    $\begingroup$ I think I'll take my chances with the unwrapped one. I don't know if I have enough control over the other one to not accidentally touch it myself. And if my opponent has the wrapped stick, I'll probably just slam mine into his as hard as I can and hope he poisons himself, since his body is closer to the poison than mine is. $\endgroup$ – Erik Jun 2 '15 at 19:30
  • $\begingroup$ It also skips the step of wrapping the jellyfish around the branch in the first place. There's a good chance you'll not reach the battlefield simply because tightly wrapping a jellyfish around a branch without touching it is pretty difficult. $\endgroup$ – Erik Jun 2 '15 at 19:32
  • $\begingroup$ You don't have to wrap the entire Jellyfish around the stick - just cut off the tentacles and use those. Wearing really thick gloves is likely enough to not get stung while wrapping it. Your statement regarding the positioning of the poison in relation to the user vs the victim is also flawed - does that mean we shouldn't use handheld tazers either, because we're closer to the tazing portion than the enemy is? People wouldn't have used swords either, by that logic (Or knives, or anything sharp). $\endgroup$ – Aify Jun 2 '15 at 19:39
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    $\begingroup$ All of those weapons aren't fatal on an accidental touch. And if you have really thick gloves, you have the material needed to make slings, which are much better than jellyfish wrapped around sticks. $\endgroup$ – Erik Jun 2 '15 at 19:50

Isn't the obvious answer to arm your Jellyfish with the everything it is lacking?

Introducing the Jellyshark!

You thought scientist learnt their mistake when crossing a Shark with an Octopus. But the folly of man is unlimited. In the darkest labs of government research comes to Jellyshark!

Scientists have managed to isolate the Jelly part of the Jellyfish and successfully removed the 'fish' part and replaced it with a SHARK!

The result is an invisible and highly poisonous version of the Sharktopus!


Send torpedoes filled with jellyfish into submarine propellers until they wear away

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    $\begingroup$ Welcome to worldbuilding.SE. When you have a moment, please take our tour and visit our help center. I'll give you credit that this actually does answer the OP's question, but we prefer answers with some meat on the bones. For example, what are you saving by using jellyfish? You are, after all, still building the torpedo, which I assume is the same other than the warhead filled with jellyfish? The answer could use some details. Cheers! $\endgroup$ – JBH May 3 '18 at 2:09

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