Here They Come!

The outburst of 1st Generation butterflies is beginning.

Image of Monarch Butterfly in early May in Minnesota — This female in Wisconsin is one of the week's northern-most monarchs. Sighting and photo by Chris Smith in Hudson, Wisconsin on May 14, 2017

Moving into Minnesota

After a 3-week lull, the migration advanced to latitude 45°N this week. Observers in Minnesota were ready and waiting to welcome the monarchs.

"One adult flying around the Driskill's grocery store and by the library at high speed, about single story roof height. Unable to pinpoint male or female. It was bright, definitely not a Gen Zero (from Mexico)," wrote Patti Keiper from Hopkins, MN on May 14th.

Eggs Across the Landscape

Since their arrival in Texas in March, we've watched for two months as the monarchs from Mexico have laid eggs across the landscape. Now, we're beginning to see the explosive growth of the 1st spring generation. Over the summer breeding season, the population will increase with each new generation.

One monarch could produce a billion butterflies in only 4 generations if all of her eggs survived. In this week's slideshow, explore the limiting factors that keep the population from growing exponentially.

Migration maps comparing last week to this week May 9 and May 16, 2017

From 43°N to 45°N

Laying Eggs in MN

How Does the Monarch Population Grow?

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

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.

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.

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.

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.

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!

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!

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?

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?

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;

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;

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.

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.