Monarch Butterfly Migration News

Monarch Butterflies

Monarch Migration News: May 12, 2016
By Elizabeth Howard

Monarch enemies take a big bite of a monarch's potential offspring, so how does a population grow?

"Observed an Argentine ant remove a monarch egg off of a narrow-leaved milkweed stem and carry it down the plant. I do not know if the egg was hatched or not." — Katy Kughen Vista, California

News: Waiting for the Surge

The lull between generations continues. With only 18 sightings reported during the past week, we're still waiting for the 1st generation to come out in full force. The first half of May is always the slowest time of year, and this year is no exception.

Sightings Down
Overall this spring, the number of sightings reported to Journey North has been lower than in all of the past 5 years, except 2013.

The low level of spring sightings — coupled with photographic evidence of returning monarchs in unusually poor condition — suggest that the March storm in Mexico caused high levels of mortality and morbidity. Were it not for the storm, the number of sightings this spring should be higher — particularly compared to the past 2 years — given the relatively large size of this winter's pre-storm population.

Looking Ahead
Dr. Chip Taylor summarized his predictions for population recovery in a recent post to Monarch Watch:

"The conditions in Texas for reproduction by these returning monarchs are key. Successful reproduction in the South Region depends on the temperatures in March-April, the number and distribution of milkweeds and nectar sources, the abundance of fire ants, and other factors. These conditions vary from year to year but have a significant impact on the number of first generation monarchs that move north from this area in May and early June. The size of this first generation moving north will largely determine the degree to which the population will be able to recover from the losses incurred during the late-winter storm."

Sightings Down

Reproductive Potential

How Does a Population Grow?
Teaching Suggestions

One female can lay several hundreds of eggs. Let's see how quickly the numbers could grow from one monarch generation to the next.

How Many Survive? One female 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: Temperatures can be too hot or too cold; Precipitation can be too high or too low; Enemies can be many or few; Diseases can be deadly or mild. Food sources can be scarce or abundant...

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; Enemies can be many or few; Diseases can be deadly or mild. Food sources can be scarce or abundant...

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.

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

Report Your Sightings


First Adult report \| map \| list	Milkweed report \| map \| list	What to Report Report
		After first sightings, continue to report all monarchs — adults, eggs, and larvae.
First Egg report \| map \| list	First Larva report \| map \| list

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Next Update May 19, 2016