In this world there has been a recurring population surge of ferocious insects every 20 years for many centuries. The setting is approximately our own time in relation to the existence of "cave men". In other words, since around the time humans began to create things and have fire, essentially stone age technology, there has been a plague of insect attacks which very nearly destroy the population every 20 years. Consider the cicada: https://en.wikipedia.org/wiki/Cicada and the locust: https://en.wikipedia.org/wiki/Locust merging the two behavioral characteristics into a larger insect which feeds primarily on humans. Possibly feeding on other mammals as well, presumably due to the weakness of exposed skin and that they are warm blooded.

How far could human civilization progress given this hindrance in individual development? If they were able to advance similarly, how would civilization be different? How might humans evolve over this time span?

I am looking for answers which are realistic, but some creative leeway is allowed. No explicitly magical answers please.

Points to keep in mind (derived from answers):

  • The insects have a life-cycle like a cicada and feed like locusts but on flesh.
  • The adult insect is slightly smaller than your head (not including wings).
  • Humans are a prime target but the insects feed on other warm blooded creatures
  • The eggs and larval stage exist in hidden and spread out locations, under ground or deep in caves.
  • The attacks are horrible and many people die, but there are enough survivors to keep the human population from going extinct.

Edit: Not just any Cicada, specifically the Periodic Cicada: https://en.wikipedia.org/wiki/Periodical_cicadas

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    $\begingroup$ I'm having a hard time seeing how this could possibly be answered to hard-science standards. Do you really want that tag on this question? $\endgroup$
    – user
    Dec 24, 2018 at 20:36
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    $\begingroup$ "decimated" so one tenth of the population wiped out once every two decades then? I don't think that's going to cause much of a problem or slow us down any, it would just mean we could afford to have one less really good homicidal war among ourselves during that period. $\endgroup$
    – Pelinore
    Dec 24, 2018 at 20:47
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    $\begingroup$ Are you using the literal meaning of "decimate" or some greater loss of population? $\endgroup$
    – Separatrix
    Dec 24, 2018 at 20:48
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    $\begingroup$ "There are lots of dangerous things on this funny little planet of yours, Clara...most of which you eat" -- Doctor Who. I see insect recipes in their future. $\endgroup$
    – user535733
    Dec 24, 2018 at 22:16
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    $\begingroup$ Sounds similar to the Stargate: Atlantis plot for the humans in that galaxy, with up to 50 years between cullings. Except in this Q, insects are stopped when people invent screen doors, or start keeping flocks of insect-eating birds (or frogs, or bats, etc...) just waiting for the insect plague "dinner bell". Like our society has pet cats everywhere, they have birds $\endgroup$
    – Xen2050
    Dec 25, 2018 at 1:58

5 Answers 5


Presumably the insects swarm, gorge, breed, then either die or hibernate. Then come out in force 20 years later after the eggs have hatched and the larvae mature into adults who can fly and who need human blood in order to support breeding.

Humans have 20 years to find and kill the eggs or to kill the larvae. If the eggs are grouped together, then fire is something even primitive peoples can handle. If the eggs are in clusters but the clusters are spread out, lots of kids with pointy sticks will do the trick. If they're very spread out or in inaccessible places, it's harder.

This should reduce the population of killer insects enough that more humans survive. After a few generations, there are fewer eggs/larvae to kill and more humans to do it.

The pressures to do this more efficiently will help drive technology, communication, education, and more.

All the things in other answers will come into play:

  • Better housing (or at least strong shelters with a water source and food storage to last a few days or weeks)
  • Protective clothing
  • Food preservation
  • Calendars
  • Methods to predict the swarms
  • Surveillance techniques to know when the swarms have gone
  • Containers to store food and water
  • Indoor cooking methods
  • Light sources
  • Ventilation methods
  • Understanding geology and movement of water including underground sources
  • Well building

Differences with a real-life society?

  • Their religion will probably be on 20 year cycles and be focused on the plague.
  • They will be obsessed with calendars and weather prediction.
  • Material science and engineering will be advanced.
  • Exploration will be a high priority (finding a region the bugs can't get them).
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    $\begingroup$ Very nice, this answer is the closest to the format I was looking for so far. And yes, the eggs are clusters, very spread out, in inaccessible places, probably underground. Actually I am starting to think the insect swarms come out of the very caves the humans might have sought shelter in...they might be moving to colder climates to get away from these things $\endgroup$ Dec 24, 2018 at 21:52
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    $\begingroup$ Actually this is pretty close to reality - areas that were subject to massive insect invasions, such as locusts, learned to build with stone and mud. They learned to store extra seed for the bad years, and their water cisterns carved from stone still hold water today. $\endgroup$
    – pojo-guy
    Dec 26, 2018 at 18:17

No advancement at all

Let's assume "very nearly destroyed" (a very vague description) means less than 5% of the population survives every attack. Those attacks occur every 20 years. Let's make an outrageous assumption that the only remaining people are distributed 19:1 in favor of women and all the women are prime childbearing (18-20 years old).

In 10,000 BCE the world population is estimated to be 2.4 million. The late stone age was about 40,000 BCE, let's assume 1 million people. The insects kill 95% of them.

That's 50,000 people: 2,500 men and 47,500 women. Let's be generous and say each woman has an average of 10 children (we're being outrageous, after all) before their bodies simply can't take any more. I'm not going to get too detailed, I'm assuming no generation produces within the time boundary of another. This means that when next the insects come, we have a population of about 525,000. That's HALF of the original count — and that's important.

Because the insects take 95% again. I'm ignoring accidents, war, plague, and anything else that can kill a human. I'm assume 10 kids, no miscarriages, etc. Just the insects.

Now we have only 26,250. Magically, 24,938 are women.

Another cycle. Now we have 13,781...

See the problem? We're being OUTRAGEOUS with humanity in giving them far beyond the normal possibility of surviving. In reality, they're extinct in 200 years. Max tech level: stone age. In fact, they probably regressed.

So, how much damage can my insects do and have growth?

A better child-bearing average is 4. I'm still going to ignore war, accidents, miscarriage, illness, and everything else (completely unrealistic, but enough for government work, as they say). I'm also not going to play the overlap as that woudl require more calculation than I want to put into it. The odds are you have basically a 1:1 distribution of men to women. Realistically, some would be too young to breed, others too old, but let's ignore that, too. How many can the insects take and have any population growth at all?

(1,000,000 * X)*4/2 = 1,000,000 X = 50% MAX!

Anything less than a 50% kill rate and the human race is extinct. It's just a matter of time. In reality, accounting for everything I said I was ignoring, your insects probably can't take more than 40%. I'm going to roll with that.

Now, how much can we take and end up at, say, steam engines? Practical application engines came in the 1700s. Let's say 1700 for easy math. 40,000 - 1700 = 38,300 years. Insects every 20 years. 38,300 / 20 = 1915 generations.

MASSIVE ASSUMPTION: If I end up with 50,000 people, I have a (barely) believable chance of inventing steam engines. So, I start with 1,000,000 and end with 50,000. How many can I take over 1,915 generations to get to this?

I hated my statistics class...

My gut says it's about 42% maximum.


What tech level humans can get to isn't really the question you want to ask. You can get to any tech level if the insects destroy few enough people every 20 years. Therefore, the real question is, how many people can my insects destroy every 20 years and get to a specified tech level?

Steam engines: ~ 42%


  1. Any declining population will result in extinction eventually.

  2. Any advance in technology provides better protection against the insects.

Franly, once we have fire (smoke) + caves, we have a way to save most of the people on every attack.

Final conclusion

By the stone age people can protect themselves. I've talked myself out of the believability of this scenario. Sorry.

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    $\begingroup$ I gave you a point for the maths. You have offered some great points on how civilization would be altered. $\endgroup$ Dec 24, 2018 at 21:48
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    $\begingroup$ No we don't all have to die in this story. But the horrors of the attacks would surely shape civilization. $\endgroup$ Dec 24, 2018 at 22:37
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    $\begingroup$ I'd say even the most pessimistic conclusions here are still far too optimistic. Even if the mortality rate from the insects were low enough not to just wipe people out. There would be virtually zero civilization progress. Rather, there would be no civilization. We'd be hunter gatherers forever. Civilization only happens when people can settle down and become farmers who can produce just a little bit more food than they need and people find themselves with some free time to specialize. $\endgroup$ Dec 25, 2018 at 10:11
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    $\begingroup$ More likely, since these insects would have evolved along side our ancestors, humans probably wouldn't have evolved in the first place as critters with big brains, high maternal mortality, and long infancy would probably not be advantageous. So, there would be no civilization or technology of any kind invented ever. $\endgroup$ Dec 25, 2018 at 10:14
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    $\begingroup$ To add to this answer and Shufflepants' response: you'll have a scenario where mammals and humans have evolved survival mechanisms against the horde (where only a very small percentage of the population dies), or mammals all die out, eventually leading to the death of the locusts themselves as well! $\endgroup$
    – stux
    Dec 25, 2018 at 15:44

Insects are both bane and boon... and much worse for low-tech than for high-tech.

They're not ever going to knock people back down the technological totem pole, because 20 years is well within living memory. Any technology is going to be build with the assumption of once-every-20-years horrible insect swarms. Mostly, then, it adds another thing to the list of fundamental human requirements. You need food, water, oxygen, shelter, and protection from the bloody insects.

The insects cannot possibly mostly feed on humans, because the humans are pretty much guaranteed to figure out ways to not be easy targets to insects of this variety, which means that there won't be enough human-based food resources in the environment for them to sustain the horrible ravaging swarms.

So first you need to have the cavemen adapt to this, or the species dies out as a whole. Once you've got that, though, it's a matter of making sure that all of your buildings are insect-proof, and that every twenty years you've built up enough food to survive without going out much. For those times when you must go out into the swarm, people would be developing particularly thick clothing (leather, say) and facemasks - leave no skin exposed. The folks most likely to die would be the particularly poor - those too poor to have stored up food, or to have the thick clothes necessary to go outside in search of more. You might even have people learnign how to harvest fromt eh swarm itself. There are certainly places where locusts are eaten.

You might see some technological slowdown, as it would take resources out of the economy, and technology has often been driven by nobles showing off using excess resources. Still, there's nothing saying that they couldn't get as far as we are now, just with somewhat more well=protected houses.

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    $\begingroup$ Good point about the food source needing to support the population of insects. It would need to be a larger group including most warm blooded animals possibly. The swarm of insects will need to look like clouds of locusts so they are going to need a lot of food. $\endgroup$ Dec 24, 2018 at 20:59
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    $\begingroup$ @takintoolong that's the thing, though. You wouldn't have "most everyone is killed". Swarms of flesh-eating insects are an environmental threat, but not an insurmountable one. You just need food stores, reliable shelter, and possibly thick clothing. If you give humanity thousands of years, they'll figure that stuff out. If you give the insects thousands of years in which humanity hasn't figured that stuff out, they'll wipe out the species entirely, unless the insects are limited to a specific temperate zone. $\endgroup$
    – Ben Barden
    Dec 24, 2018 at 21:12
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    $\begingroup$ If the insects are limited to a specific temperate zone, then humanity will build some sort of society in its outskirts, will learn about the insects and preserve the information in the enclaves outside that zone, and then you're back to having food stores, reliable shelter, and possibly thick clothing. You can't really have it both ways. Either they're initially utterly lethal, or they can be largely overcome once we've developed a bit. $\endgroup$
    – Ben Barden
    Dec 24, 2018 at 21:14
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    $\begingroup$ @takintoolong ...in which case all the humans will die. That's the other side of that pendulum. Thing is, if they can advance at all, then that advancement will help them out for the next time. They're not going to advance a certain amount and then hit a wall. They're not going to get a certain distance and then get knocked back. After a few thousand years, either it's an obnoxious-but-manageable issue that everyone already knows how to deal with, or it killed us all back at the beginning. $\endgroup$
    – Ben Barden
    Dec 24, 2018 at 21:24
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    $\begingroup$ @takintoolong, there will be lots of elders. The survivors of the first swarm will remember it, and this memory will give them greatly improved odds of surviving the second swarm. By the time the third swarm comes around, these people will be in their 60s, 70s, and 80s, and will be experts on surviving -- and they'll pass that knowledge on to their children and grand-children. If humanity survives the first wave or two, the "civilization-destroying" insect swarms will be merely a major problem, not an existential threat. $\endgroup$
    – Mark
    Dec 25, 2018 at 6:36

Sorry I can't comment on previous answers reputation too low but.

Bug repellent comes to mind, which may have already been a possibility to prevent mosquitoes 77,000-38,000 years ago? As there must be some plant that the bugs can't stand the smell or taste of or an oil or sap that could be used.

http://www.earthtimes.org/scitech/plant-insect-repellent-stone-age/1697/ https://en.wikipedia.org/wiki/Timeline_of_historic_inventions [74]

Wadley, L; Sievers, C; Bamford, M; Goldberg, P; Berna, F; Miller, C. (2011). "Middle Stone Age Bedding Construction and Settlement Patterns at Sibudu, South Africa". Science. 334 (6061): 1388–1391.

Colder weather may also help as Humans could migrate to colder areas during the attacks.

Or pushing a bolder in front of your cave/shelter entrance providing the bugs are not in that cave.

Handmade bricks came much later, 6000-7000 BCE https://www.explainthatstuff.com/timeline.html

So I don't see a reason why there would be no advancement, but that it could be more delayed. It could possibly even encourage advancement by decreasing the time to have larger communities gathering under shared communal shelters.

I would expect large covered shelters to be made, with retractable sun roofs and later glass windows.

Later should the breeding cycle can be interrupted on a large enough area the insects could be wiped out.

Can widespread outbreaks be prevented? Such as in real life. https://motherboard.vice.com/en_us/article/z43x7a/how-to-stop-a-plague-of-locusts

This would make a great concept for story/movie/game would love to see this progress further.

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    $\begingroup$ Plus one for the stone age bug repellent. I also started thinking about the game concept. Actually the way you wrote that is the order my thoughts progressed, first a story, then how it could be a movie, and then a game lol. $\endgroup$ Dec 25, 2018 at 16:06

Migration is the obvious answer to start with. Once it starts getting close to time, the tribe and it's livestock move into cold/mountainous regions where the insects don't go.

As time goes by they develop food storage and barricade themselves in caves to wait it out and them barricade themselves in purpose built structures. They might also build rafts and ships and move out to sea to wait them out.

Like all things, evolution will favor those who are adaptable. I doubt it would slow human development down much.

  • $\begingroup$ Good point Thorne. I think it would take a few passes for them to realize the pattern first though. Then initial migrations won't be very successful because at first they won't go far enough and the insects can fly. Ultimately, the humans will figure out how to survive, but they will have to alter their behavior and deal with other difficulties which our own ancestors did not. Much of the prime real estate will not be settled until later, and settling down might first occur in areas not conducive to civilization as we know it. $\endgroup$ Dec 26, 2018 at 23:53

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