From Eggs to Butterflies
How Does a Population Grow?


How Many Survive?
A female monarch butterfly can lay hundreds of eggs. What would happen if every egg survived? Let's see how quickly the numbers could grow from one monarch generation to the next.

What is a Generation?
A generation is one complete life cycle. A monarch can complete its life cycle in only one month. Let's count monarch generations and see how long it takes to reach a billion butterflies.

One Billion Butterflies
If all of her eggs survived, one monarch butterfly could produce a billion butterflies in only 4 generations. She would have over a billion great-great-grandchildren!

What Limits Monarch Numbers?
You may like monarchs, but the world would be swarming with butterflies if all of their eggs survived. With such a high reproductive potential, why don't we have billions and billions of butterflies? What factors might limit their population size?

Limiting Factors
Monarch numbers can rise and fall for countless reasons. Here are some examples of limiting factors:

  • Temperatures can be too hot or too cold;
  • Precipitation can be too high or too low;
  • Food Sources can be scarce or abundant;
  • Enemies can be many or few;
  • Diseases can be deadly or mild.

Finding the Balance
Scientists are still learning about the balance between the monarch's high reproductive potential and the factors that limit the population's growth. Perhaps only 2% of all monarch eggs become butterflies, yet the population typically gets a little larger with each generation. You can help scientists learn more about monarch populations by contributing your own observations.

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