I have a species of creatures that live in packs off the coast of my fictional world's one super continent. Humans have lived there for millions of years. At one point these humans had achieved the level of technological domination that we have over Earth. They mercilessly exploited resources and mixed species that should never have even met on a regular basis.

They generally screwed many ecosystems up. At some point the planet was unable to support them any longer. With no more resources left to exploit, human society collapsed. Rather than banding together to exploit the stars, humanity fought itself, with powerful individuals scrambling to ensure their place when the chaos ended. Over time, with no oil, or coal left, electricity became a rare commodity reserved for the powerful. The population plummeted from 10 to 1 1/2 billion. Because of these events technological progress stagnated. Literacy dropped. The world was stuck at mostly pre-industrial levels of technology.

Over millions of years species began to evolve to take advantage of the weaknesses the humans presented. Evolution caught up with humanity. Predators hunted humans for prey in many regions.

I want a creature in the oceans to evolve to eat voyaging humans. What characteristics and features does this creature need to survive and thrive? It will be very large, but not as large as a Spanish galleon. It will be a lone-hunter. I guess it would also have to be able to go for an extended time without food. It cannot go on land. Humans have to be its primary food source.

If this is too unrealistic, please tell me and tell me how I can improve my world. I have also tagged in this event.

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    $\begingroup$ Would humans have to be numerous in the ocean for them to be the primary food source of an ocean-bound predator? $\endgroup$
    – Frostfyre
    Commented Dec 3, 2015 at 17:36
  • $\begingroup$ @Frostfyre I was thinking that the animal would be delling near the coasts and attack ships, poking a hole in them to cause their sinking, somehow getting the humans out after they have all drowned, or going after the manageable life boats. $\endgroup$
    – Jax
    Commented Dec 3, 2015 at 17:40
  • $\begingroup$ @Frostfyre I also wasn't suggesting that the species in question was numbering anywhere near that of the human population. I was thinking that at any point there might be 1-10 thousand, depending on conditions. $\endgroup$
    – Jax
    Commented Dec 3, 2015 at 17:45

5 Answers 5


If it had to eat only humans it would rapidly go extinct. Either humans would hunt into the brink of extinction or it would hunt coastal humans to the brink of extinction.

If it hunts only humans it would have to be able to travel up fresh water rivers and lakes and be able to travel on land at least short distances.

If it can not go on land or up fresh water rivers it needs other optional food sources. Why would a carnivore not eat other smaller prey animals when it came across them? (Unless there are no others left)

Other adaptations? Intelligence always helps. The strength to break open sailing vessels. Strong limbs or a sharp beak/claw. Otherwise humans just retreat into the ship to save themselves.

Either that or it needs to be small enough to get on the ship and into any place humans hide within it.

A poison attack? Poisoned quills that it can shoot would be ideal. Or perhaps a large blob of a mucusy ink that would release noxious vapors or incapacitate people it touched.

Tool use? If it is smart enough to use tools it can adapt to human defenses.

In many ways a more aggressive squid or giant squid would be the ideal base for this creature since it has many of the basics. Especially if it gained a higher intelligence and a fondness for the delicacy of human flesh.


Well I have a few issues and possible ways to fix them.

After millions of years humans will not likely be recognized as such. That is a long time for evolution.

So instead of evolution creating monsters that like 'long-pork' let them be genetic mutants from humanities genetic experiments, some of the more 'successful' ones.

I think it would be difficult to make humans the 'primary' food source for your monster, because people would quit sailing and/or the monsters would starve to death. So you can make people their preferred meal over any other, but they need to eat some "fava beans and a nice chianti" between the courses of human liver.

But any kind adaptation could work. Maybe there are 'mermaid' growths on it's back that mimic humans, maybe it has long appendages to grip it's prey. Or a reinforced skull to smash into things?

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    $\begingroup$ Have to agree with the comments regarding timeline - it's just too unlikely that any kind of human society could exist relatively unchanged for the millions of years required for creatures to naturally evolve into the kind of predators you're describing. You need some kind of accelerating factor, like the genetic experiments described - or perhaps there is some kind of environmental pollution that causes accelerated evolution, or perhaps this planet has a much higher level of background radiation (causing mutation and therefore evolution) that humans are somehow immune to. $\endgroup$ Commented Dec 3, 2015 at 19:50

Chameleon skills: The predator is at risk of attack by humans because they can injure or kill it with any sharp objects or projectiles they have on hand. Therefore, it would be helpful if the predator could approach and attack before it is detected. If it is a proto-cephalopod, it could be able to camouflage itself by changing its coloration the way octopi and squid do. It is not too far-fetched. Some fish can do that. So can some reptiles.

Unusual biology: If it could digest cellulose it could approach a human-piloted watercraft and eat the whole thing, sailors and all. At present, no mammal can digest cellulose all by itself. Those that do consume wood are hosts to micro-organisms that excrete chemicals that can dissolve cellulose.

"Animals such as cows, horses, sheep, goats, and termites have symbiotic bacteria in the intestinal tract. These symbiotic bacteria possess the necessary enzymes to digest cellulose in the GI tract." Source: http://chemistry.elmhurst.edu/vchembook/547cellulose.html

General ruckus-causing: The predator's need to maintain a healthy level of such bacteria could motivate it to make various forays and assaults on many features and denizens of the story's setting. That gives it more air-time and makes it more fearsome.

Kidnap: If it is intelligent, it could maintain underwater caves or other structures that trap large air bubbles in which human prisoners it catches and transports. Underwater, with a modest air supply, they can be kept cool and alive until he is ready to eat them. Some prolonged imprisonments would give the humans time to regroup and plan a rescue.

  • $\begingroup$ Nice, a multiplicity of choices - to be fair, by modern standards, the question might need to be closed as being too broad, needing narrowing down, as it's fishing for ideas. Welcome to wb.se, take our tour, and read-up in our help center about us. Enjoy the site. $\endgroup$ Commented Feb 22, 2021 at 22:00

Your species won't be able to function as it is currently written. Humans in general are a terrible prey choice for a predator that is specialized on hunting a single type of prey. Humans are slow-breeding and rely on extremely low infant mortality rates in order to maintain a viable population. The only reason humans have an overpopulation problem now is that we don't have any reliable means of population control, and so even our painfully slow reproductive rate allows us to multiply like rabbits without any external checks on our numbers. Add in an actual predator that could reliably prey on us without being wiped out and our numbers would rapidly dwindle. Any predator that preys solely on humans would have to exist at extremely low population densities in order to function or else risk exterminating its food supply.

On top of this, humans have a tendency to deal with predators through campaigns of proactive violence. One of the first things large human populations tend to do when they establish themselves in an area is systematically wipe out all of the megafaunal predators. This is mostly because humans are very bad at defending themselves if caught by surprise, and rely on campaigns of proactive violence to maintain a buffer zone between the predators and their settlements where they are most vulnerable or have vulnerable offspring. A species which preys only on humans would be at the top of the extermination list and would be killed whenever possible. Humans have wiped out entire species just because we've thought they might be a threat to our farm animals, how do you think we would react if an animal was a threat to us directly?

On top of all these issues is the fact that your species is specialized to feed on an animal which doesn't even normally occur in its environment. On land you could at least make the argument that a predator could seek out and hunt down humans, but the only humans travelling on the water are going to be either sailors, fishermen, or swimmers, a mere fraction of the human population. There simply wouldn't be enough humans travelling on the water to be a viable food source. This is even before you consider humans just plain avoiding water travel because they know its dangerous. If all of the humans in an area avoided boat travel for a couple of years, your species would starve to extinction.

An animal the size of a Spanish galleon also wouldn't be able to survive on a diet of rare humans alone. A Spanish galleon is about 30-50 m long, and the largest carnivorous whale, a sperm whale, is only 20 m at maximum. Assuming similar body proportions to a sperm whale but scaled up to the size of a Spanish galleon and a cold-blooded metabolism of a saltwater crocodile, your predator would weigh approximately 1600 tons (1.45 million kg) and require 525000 kilocalories per day (noting this is a very approximate estimate because estimation equations get wonky when you extrapolate them to kaiju size). Scaling that by the number of calories in the human body, which is about 125,000 kcal, and your predator would have to eat two and a half humans every day just to sustain its energy budget. This is assuming your predator does not waste any energy hunting food. The amount of energy required per kg would be low, but the total energy needs would still be enormous. It wouldn't be enough for a species to survive.

On top of that, you have growth to consider. Your predator has to actually reach 30 m (and now that I think about it, it's not clear what they would eat when they are young and cannot sink ships and are possibly too small to even eat infants). Growth is a trade-off between how much metabolic energy you burn and how fast you grow. Crocodiles, for example, grow incredibly slowly and can take in excess of 50 years to reach monstrous sizes. Giant extinct crocodiles like Deinosuchus and Purussaurus are thought to have lived over a century. By contrast, whales and dinosaurs reach maximum size in less than a decade but have very high metabolisms. Given your species incredibly meager energy budget, it would have to have an incredibly slow growth rate to survive on its meager diet. This would make your species very vulnerable to being hunted to extinction by humans. Slow-breeding, long-lived species generally don't do well when humans are around.

A much better option would be something like crocodiles, sharks, or goonch catfish. Normally feeding on thinks that are abundant in an aquatic ecosystem like fish and turtles, but who have become accustomed to viewing humans as food due to human behavior (like burying their dead on funeral pyres or dumping waste offal from slaughterhouses into the water). This would cause your predator to associate humans with food and therefore seek out humans when they are hungry. It would also cause them to disproportionately associate themselves with human settlements, as the humans are unintentionally encouraging them to stick around by providing them with free food. All the predator needs to do is be smart enough to avoid being hunted.


It would need a specific adaptation that is vastly improbable: an obsession with eating humans.

Most predators eat whatever's handy. This one is even targeting prey that doesn't live in its habitat, and it has to destroy the boat (expensive in calories) before it eats. Furthermore, a large animal that goes a long time between meals needs to have large meals. (A cold-blooded animal, definitely; that needs a lot less calories.) Furthermore, humans are not biochemically distinctive enough that you could make your creature an obligate human-eater.

Hypothesizing that someone genetically engineered it as a killer, the "primary" aspect is one that would be selected against. It would have to eat other things because the genetic engineer would not want it to die out waiting for the next ship when it could be eating other things and waiting. Then, the greater ease of eating other aquatic species would be selected heavily for, as those who eat the most of them get more calories for less effort and so leave more offspring.

Were there an actual species in the ocean doing this, I would suspect that a monster-making machine was pumping them out. They would not need to thrive because they would be continually replaced.


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