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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

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).

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.

Conclusion

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%

BUT!

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.

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.

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.