In 1875, trillions (yes, trillions) of Rocky Mountain locusts swarmed over the western United States. Thirty years later, they were extinct.
The Rocky Mountain locust must be one of the fastest boom-to-bust species in world history. Throughout the 19th century CE, these locusts descended on the western United States in enormous swarms that consumed vast swathes of crops. They blocked out the sun, ate the clothing off people’s backs, and burrowed deeply into the popular consciousness. It was a repeating natural disaster, brought about by that century’s rapid intensification of farming.
(A side note: in academic research about disaster management and recovery, it is noted that a natural event is only a disaster when it affects us adversely. While we cannot control certain events, it’s actually our decisions that turn them into disasters. In other words, you can call a flood a natural disaster, but if you build on a floodplain then it’s not entirely the flood’s fault.)
In one famous incident, a physician named Albert Child attempted to calculate just how many locusts were in a swarm. He measured the speed of the swarm’s progress, multiplied it by how long it took to pass him by, and came up with a ballpark figure in the trillions: between 3.5 and 12.5 trillion locusts spread across half a million square kilometres. That’s… well, that’s a heck of a lot of locusts.
Farming, though, was also the locusts’ demise. Farmers switched to different crops that were harvested before the locust swarms arrived. The locust breeding grounds, in the sandy riversides near the Rocky Mountains, were plowed up and trampled down by expanding agriculture. Thirty years after that famous swarm, the Rocky Mountain locust was extinct.
[Thanks to Gareth E. for suggesting this topic.]