How Does a Population Grow?


From Egg to Butterflies
What if all monarch eggs were to survive to become adult butterflies?

How Many Survive?
A female monarch butterfly can lay several hundred eggs. 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?
With such a high reproductive potential, why isn't the world swarming with billions and billions of monarchs? What factors might limit the population size?

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

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

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. Probably less than 1% of all monarch eggs become butterflies, yet the population typically gets a little larger with each generation.

Report Your Sightings
You can help scientists learn more about monarch populations by contributing your own observations.