Would humans quickly exterminate man-eating predators?
Actually there have been megafauna which preyed on humans at least occasionally for hundreds of thousands of years.
Some of the species which once occasionally preyed on humans have become extinct over the millennia, and some not. And of the species which preyed on humans and became extinct, it is not always certain that humans were responsible for their extinction. And in cases where humans drove to extinction species which sometimes preyed on humans, it is not known if that occasional preying on humans was the main reason why humans caused their extinction.
Humans who settled in an area and destroyed the natural habitat to make it better for humans could have caused an ecological collapse which led to the extinction of the normal prey animals of large predator species, and thus eventually the extinction of the predators themselves, humans not being a good enough substitute for their natural prey.
There is little evidence of the causes which led to the extinction in prehistoric eras of predators which occasionally preyed on humans. Thus there is no proof that humans exterminated some of those species, nor any proof That the motive for human extermination of those species was to prevent them from occasionally preying on humans.
Of course early men only had spears, bows, and arrows to kill large predators which occasionally preyed on humans. In historic times, and especially in the modern era, humans have had a lot of deadly weapons to slaughter dangerous animals with.
But is it true that in modern times humans always react to occasional attacks on humans, and predation on humans, by exterminating those predators?
A few people are killed by American alligators every year, and some are eaten. Thus American alligators do occasionally prey on humans. And there was a time when American alligators were hunted almost to extinction and became endangered. But while some people hunted American alligators because they were potentially dangerous to humans, most hunters killed and skinned alligators for their hides, which make good leather.
But American alligators have been saved from extinction. Alligator farms were formed to raise alligators from eggs and kill and skin them when they reached the size which had the best skin. And American alligators were put on the endangered species list and it became illegal to hunt them. In recent decades the numbers of alligators have multiplied, and thus the frequency in which they attack, injure, or kill people has also multiplied.
And so far as I know there is no great public demand to exterminate American alligators to prevent them from ever killing any human again.
And in many poor parts of the world where weapons are not as easily available as in the rich USA, populations of people co exist with populations of other species of crocodilians, including some species which sometimes prey on humans. So I think that a few hundred people are killed every year by members of various crocodilian species around the world. And so far as I know the various occasionally man-eating species of crocodilians are not in imminent danger of being exterminated.
Among the megafauna which occasionally prey on humans, there are lions and tigers and bears, oh my, and leopards, and wolves.
And of course the numbers of those species of predators have drastically declined over the last few centuries as human populations expanded. And some of that population decline was due to humans hunting those predators because they occasionally preyed on humans, and some was due to humans hunting those predators because they often preyed on species that humans like to hunt, or preyed on domestic animals raised by humans. And a big part of the population decline of those predators was due to humans expanding their farming and grazing lands and destroying the natural habitats of those predators and their natural prey.
So it is certainly not correct that humans will immediately mobilize to exterminate any species which occasionally kills and eats humans, or that such eradication efforts are always quickly successful.
However, probably only a few hundred or a few thousand people are killed and eaten by predators each year. That isn't many considering that hundreds of millions of people live in close proximity to thousands or millions of predators which sometimes prey on humans. It is possible that is not enough slaughter to satisfy a mad scientist seeking to unleash predators upon humanity. If the mad scientist finds a way to make new and improved predators kill ten times or a hundred times as many people per year as they do now that might cause humans to fight back hard enough to exterminate those new man eaters in less than the decade specified in the original question.
That is the risk that a mad scientist seeking to unleash deadlier predators upon an unsuspecting world has to face, the risk that if predators started eating a larger number of humans, even a slightly larger number of humans, that increase might possibly enough to cause humans to make an all out effort to exterminate those "improved" man-eaters and do so in much less time than the mad scientist desires.
Hungry, hungry hippo.
What kind of man-eaters should the mad scientists design?
How about hippos which are more carnivorous than present hippos, and which are genetically altered to find human flesh tastier than any other meat?
At the present time, hippos probably kill more people than any other large African animals, merely from aggressiveness, bad temper, and territoriality. Hippos are herbivores and don't usually eat meat. But members of many herbivorous species have been known to eat meat on rare occasions, and hippos have been reported to eat meat.
Hippos which had been genetically altered to be more omnivorous, eating mostly plants but eating more meat than present day hippos, and with an special attraction to human flesh, might be seeded among regular hippos and the increase in humans they killed might not be realized to be the result of mutated man-eating hippos until the required decade was over. Thus any human effort to exterminate the man-eating hippos might not even begin until they had already been preying on humans for over a decade.
When I was a child I overheard something about a elephant that kept a human body or part of one in its mouth for a long time.
This could have been the circus elephant Rajah who kept a (detached) arm of his trainer Frank Fisher in his mouth for some time after killing Fisher in 1899.
Or this might have been the story about a European zoo elephant that allegedly killed and ate a woman who sneaked into its enclosure about the end of World War Two. The most authoritative version I could find indicated that she was killed "not just merely dead, but really most sincerely dead", if you get my meaning, but doesn't mention that any parts of her were eaten.
And there have been a few reports from India of rogue, man-killing, elephants seen with body parts of their victims in their mouths. This has been explained as the elephants holding limbs in their mouths as they pulled apart the bodies of their victims.
But in 2011 a elephant was killed which had killed 17 humans. According to the news stories, meat was found in her stomach, which was DNA tested to be human meat. Supposedly her rampage was the result of the death of her calf.
Elephants are very intelligent animals, perhaps as intelligent and emotionally complex as humans.
There is a story that when Emperor Caligula was killed in AD 41, his assassins cut off pieces of his flesh, and some ate those pieces. In 1343 the Count of Briene was deposed as ruler of Florence, Italy, by a mob which cut two of his followers to pieces and allegedly ate some of those pieces. Johann de Witt and his brother Cornelius were murdered by a Dutch mob in 1672, and their livers were allegedly eaten by the mob.
So if humans can sometimes become angry enough to eat pieces of their enemies, and if elephants possibly have intelligence and emotions as complex as humans, perhaps angry elephants might sometimes eat pieces of their enemies for the same reasons that angry humans might do so.
So if a mad scientist used genetic engineering to create slightly carnivorous elephants, and gave them an instinctive craving for some small part of the human body, and released them in the wild, the difference might not be noticed for a while. A number of people are killed in human-elephant conflicts over land, food, and water each year, and there are occasional elephants that become so angry at humans for various reasons that they hunt down and kill humans.
If the new man-eating elephants rip open human bodies to take small organs which they consider very tasty, but leave the rest of the bodies uneaten, people might interpret it as the usual mess that angry elephants can create while making certain that their victims are dead. Thus the existence of genetically-engineered man-eating elephants, instead of angry man-killing elephants, might not be realized and reacted to until the ten years are over.
The Saturday Night Live show used to have a gag about a land shark that would knock on people's doors, and say it was a delivery man or something, and if they opened the door would eat them.
I once read an urban legend - or more like a rural legend - from India or Nepal about a man-killing elephant that would sneak into villages at night and knock on doors, and kill anyone who opened the door. If that story is true it would be an example of an elephant being clever and lazy enough to do things the easiest way. Because most houses around the world are flimsy enough for an elephant to smash their way into if they want to go to the effort.
In "Black destroyer", by A.E. van Vogt, Coeurl was an alien being of human intelligence level who looked like a gigantic black cat with tentacles coming out of his shoulders. Coeurl had the power to control electromagnetic vibrations with his body, thus making him the equivalent of a very powerful comic book superhero or supervillain. Coeurl needed phosphorus to survive, and would kill any living creature to get the phosphorus from the body.
In "Black destroyer", Coeurl was a survivor of a civilized species of his planet whose civilization had fallen. But "Black Destroyer" was included in A.E. van Vogt's novel The Voyage of the Space Beagle in a rewritten form, in which it was speculated that Coeurl might be an artificial lifeform created by the advanced biological science of the natives of the planet. The creation of a race of coeurls could backfire in obvious ways, leading to the extermination of the species which created them.
So if a mad scientist could create a species with powers like coeurls and release them on contemporary Earth, they might be invulnerable to Earth weapons and might exterminate all humans. So writing a story with a mad scientist creating and releasing predators with human intelligence and coeurl powers upon an unsuspecting world would justify the predators surviving and preying on humans for ten years and more.
However, such a story would have two problems:
- making the coeurl's control of electromagnetic vibrations seem plausible or even possible
- making the mad scientist's disregard for his own safety seem plausible.
If a writer can make those two aspects seem plausible, then he or she could use genetically engineered large predators with human intelligence and coeurl powers in his story.
In the Star Trek episode "The Man Trap" the planet M-113 has ruins of an extinct civilized species. It also has a "Salt Vampire" or "M-113 creature". Salt vampires need salt and can suck salt out of the bodies of other beings, usually or always killing their victims. They also use a form of telepathy to appear like harmless or even desirable persons to their intended victims, and perhaps immobilize them with some form of hypnotic paralysis in the final stage of the approach to the victim.
The plot of "The Man Trap" has some similarity to "Black Destroyer". So I have always wondered whether the Salt Vampires were the people of the planet who had built the ruins before their civilization collapsed, as Coeurl was in "Black Destroyer", or if they were an artificial species created by the advanced biological science of the native civilization, as Coeurl might have been in The Voyage of the Space Beagle. Or maybe the Salf Vampires were created by the advanced genetic engineering of another civilization on another planet, and then beamed down to the surface of M-113 to exterminate the M-113 natives and then die out eventually from lack of salt.
So using predators with Salt Vampire powers as the predators in a story has the same problems as using predators with coeurl powers. The problem of making plausible their salt sucking abilities, and their telepathic illusion powers, and also the problem of making the mad scientist's lack of self preservation seem plausible. If a writer has answers to those problems predators with Salt Vampire powers might make good predators for such a story.