Monarch Butterfly Update: March 24, 2011
Please Report
Your Sightings!

Monarchs are pouring out of Mexico now, and the leading edge of the migration has already entered Oklahoma. Picture a trail of eggs 1,000 miles long, stretching from Michoacan to Oklahoma. What happens to all of those eggs? This week, explore the challenges monarchs face that can impact the growth of the population.

This Week's Update Includes:

Image of the Week

Monarch Butterfly Egg

First Steps

News: Pouring Out of Mexico!

"I estimate only one quarter of the original number of monarchs remain at El Rosario," reports Estela this week. "I think the last massive exodus is taking place now."

North of the overwintering region, observers suddenly began to report large numbers of monarchs heading northward last week. Find each of the following places using Google maps, then measure the distance and direction from the overwintering region:

March 18
Zinapecuraro, Michoacan
(20 N, -101W)
"I am currently sitting on my patio and watching hundreds (maybe thousands) of monarch butterflies flying over head gliding on the winds on their way north."

March 20
San Miguel de Allende, Guanajuato
(21 N, -101W)
"Hundreds in an hour or so...Many are still joined in mating positions. They were clustering in some trees near the water and then moving on over the mountain range."

March 22
Tequisquiapan, Queretaro
(21 N, -100W)
"Here they come! Monarchs were flying all over Tequisquiapan, Queretaro today. There were hundreds, eating and mating! The monarchs are on their way north, coming your way."

Eggs on Milkweed
The breeding season is underway! Here are the kind of observations people are making:

March 19: Honey Grove, Texas (34 N, -96W)
"I saw a Monarch cruising around a field of henbit. It was dropping down, I guess checking for milkweed. She was not feeding on the flowers and I did not see any milkweed in the field. She just looked like she was trying to find a place to lay eggs."

In Texas on Saturday, Mr. Aschen counted three dozen eggs. When he went back on Tuesday, he found 15 larvae but only one dozen eggs. Nearly a dozen were missing. Where did they go?

March 22: Port Lavaca, Texas (29 N, -97W)
"There has been a Milkweed Assassin Bug that has been getting some Ladybug larva. I found four of their carcasses on leaves this morning. I moved it across the yard...carefully."

Monarch butterfly eggs on milkweed

Only 1/4 Remain

Zinapecuraro, Michoacan
San Miguel de Allende, Guanajuato
San Miguel de Allende,
Monarch butterfly eggs on milkweed

Eggs Mean Monarchs!
One way to watch for monarchs is to watch for monarch eggs. Check your milkweed regularly and you'll know when monarchs have arrived in your region.

Slideshow: From Eggs to Butterflies: How Does a Population Grow?

A female monarch butterfly can lay hundreds of eggs. What would happen if every egg survived? The monarch population could go from one butterfly to a billion in only four generations! This slideshow explores the limiting factors that govern the size of the monarch population. As you track the migration, identify challenges monarchs face and the limiting factors that can impact population growth.

The Migration: Maps and Journal Page
Pre-migration map: Winter monarch butterfly sightings (January or February) Map of milkweed emergence: Spring 2011 Journal Page
Looking for Limiting Factors

Let's find out when and where monarchs and milkweed appear this spring.

The next Monarch Migration Update will be posted on March 31, 2011.