Most animals emerge and decline in cycles. One year rabbits are everywhere, next year foxes are everywhere, next year carrion, etc. Bugs/insects especially have

Most animals emerge and decline in cycles. One year rabbits are everywhere, next year foxes are everywhere, next year carrion, etc. Bugs/insects especially have odd cycles that are often not yet fully understood by humans. The danger is often with cycles that run out of control. In Michigan zebra mussels operate on a multi-year (7 year?) cycle. They'll reach a peak then decline. But each peak so far has been significantly larger than the previous one. They choke out all the mussels that are indigenous to the lakes in those peaks, then decline for a few years and throw entire ecosystems out of whack.