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Monarch Butterfly Migration Update: April 25, 2002

Today's Report Includes:

News From the Migration Trail

The migration has now clearly moved into Kansas, Missouri and points eastward at the same latitude. Scattered sightings from as far north as 40N latitude were also reported. Also of importance this week was the apparent sighting of a first spring generation monarch in Brentwood, Tennessee:

"We found one fresh monarch in our meadow today. We also saw several old faded monarchs flying around as well as one fresh one,? reported Nancy Garden on April 21st.

Warm Weather Brings on the Milkweed!
What a dramatic change from last week's milkweed map! Many observers noted the unseasonably warm spring temperatures from April 14-20 as the map on the far right shows. It was almost 10F warmer than normal across much of the monarch's breeding range. (These maps are only available for U.S. data.) Significantly, of all the milkweed reported since February, 36% of the sightings occurred during the past 10 days.

Last Week

This Week

Warm Temperatures

New Generation Now on the Wing in Arkansas
Challenge Question asked you to predict when the monarch adult would emerge in Arkansas from the egg laid on March 27th. "I think Jim Edson's #1 monarch of the next generation will emerge on the 1st of May," predicted Collin, a 3rd grader at McKnight Elementary in Pittsburg, PA.

Nice estimate, Collin! Let's check in with Jim. The drum roll please...


"The first monarch, a female, eclosed about 7:45 this morning (4/22). It was a nice Earth Day surprise. Here is a photo of me releasing her." Within 2 days, another of her 37 siblings had eclosed, just in time for Jim's trip to El Dorado, Arkansas to do a monarch presentation for a 7th grade life science class. "We should have plenty of new monarchs to release after school to start the next leg of their Journey North!!! The ones I took to my granddaughter's kindergarten class should be eclosing tomorrow or the next day. We are planning a release at her school Wednesday afternoon," he wrote on Monday.

Monarch Life Cycle
by Jim Edson, University of Arkansas




April 2
2nd instar larva

April 5
3rd instar
(just after molting from 2nd instar)

April 9
4th instar larva




April 9
5th instar larva

April 13
forming chrysalis

April 13

April 22


On the Lookout for Fresh Wings?
Test Your Talents

It took 27 days for the monarch in Arkansas to develop. This map shows when and where the 1st spring generation should emerge, if we assume it takes about one month for monarchs to develop.

As you can see, fresh butterflies should now be appearing across the state of Texas, and in Louisiana, Mississippi and even Arkansas. Please watch for them! Because monarch wings become worn and faded over time, wing condition can be used to approximate age. Harlen and Altus Aschen captured the 3 monarchs pictured below in their backyard. Look carefully at each butterfly, and read and the descriptions the Aschens gave them. (See below.)
Challenge Question #25
"Which fade value do you think matches monarchs #1, #2, and #3?"
(Click on image for a closer look.)




  • Fade = 0: New, recently emerged.
  • Fade = 2: No holes, no tattering, but beginning to have missing scales to cause fade.
  • Fade = 4: Very faded, some tattering and holes. Orange beginning to turn gray, black just beginning to turn charcoal, but not yet transparent or "ghostly".

(To respond to this question, please follow the instructions below.)

Thoughts for Earth Day 2002
In recognition of Earth Day, our "Signs of Spring" report this week reflects on human population growth, and its impact on the natural world. As the graph to the right shows, beginning in about 1750, the Industrial Revolution improved the standard of living so dramatically that the human population began to grow exponentially. In less than 250 years, world population went from under 1 billion to 6 billion people. At current growth rates, we add one million more people to the planet every 5 days. How have humans managed to populate the entire globe? Learn about human invention and population growth from an historical perspective:

What if Monarchs Ruled The World?
Challenge Question #26
As we have seen, a single monarch can produce hundreds and hundreds of offspring. What prevents the monarch population from expanding as dramatically as humans have? Given adequate resources, and no disease or predators, all populations increase exponentially. So what do you suppose happens to monarchs?

Challenge Question #26
"At what stage of their life cycle (egg, larva, chrysalis, adult) do you think monarch mortality is highest?"

(To respond to this question, please follow the instructions below.)

Try This!
Imagine monarchs taking control of the world and changing it to fit their needs. They would not need schools or houses, roads or cars! What do monarchs need to survive? How might they curb death rates and increase birth rates, the way humans have? Write a descriptive paragraph telling what the ideal monarch world would look like. What inventions would be needed to make the whole planet habitable for them? Please send us your descriptions:

Reader Concerned: Will Bt Spray for Gypsy Moths Affect Monarchs?
Christine Ballenger wrote last week from Illinois, "Our Forest Preserve District plans to begin spraying several preserves in DuPage Co., Il. for gypsy moths using a bacterial spray that kills larva called Bt. They know it will kill any feeding butterflies or moths but are desperate to preserve the trees. They were told that pheromone flakes will not work unless they are used in conjunction with the Bt spraying. I am very concerned about migrating monarchs and other native butterflies not to mention what might happen to bird and? amphibian populations that eat the dead butterflies and moths. What is your position on this issue?? I would like some information to give to the commissioners. Thanks and please hurry. Spraying begins in two weeks!"

If you were a butterfly expert, how would you answer this question? Before reading Dr. Oberhauser's response below, learn about the gypsy moth life cycle and the pesticide, Bt. Then describe how you think monarchs would be effected.

Here is Dr. Karen Oberhauser's response, "Monarch larvae (or larvae of any other Lepidoptera) exposed to the Bt spray will be killed, and the number of non-pest lepidpteran larvae that will be exposed to this source of mortality is probably very high. It is unlikely to affect monarch adults, and also should not affect amphibians or birds (or any vertebrates) that eat the dead insects.

"This is an extremely difficult issue. Gypsy moths have decimated eastern forests, and are likely to do the same in the upper Mid-west. Like many pests that humans have spread around the globe, they have few natural enemies here. Careful monitoring has slowed their spread down, and is certainly preferable to the broad use of insecticides such as Bt. If few gypsy moths have been sighted in your county, it seems premature to spray. There are problems with the spraying: Ken Raffa, a UW-Madison professor of entomology, has said that Bt has had only limited success in most areas. Widespread use of Bt also raises fears that insect pests such as gypsy moths may develop resistance. However, there don't seem to be any good alternatives yet."

Discussion of Challenge Question #23
When Do Monarchs Disappear?

We asked, "If you were standing on the ground, do you think you could see a monarch 102 meters high in the sky? How could you test this without leaving the ground?"

Mrs. Nunnally's second grade class in Bedford, NH came up with several creative tests including these:
  • Measuring a kite string 102 meters long, attach a paper butterfly to the kite, fly the kite with all the string, and look for the butterfly.
  • Have someone go up in a building that is 102 meters tall and put a butterfly in the top window and check if the people on the ground can see it.

We aren't quite as adventurous as those New Hampshire students. We pictured making a life-sized butterfly and testing visibility on the school grounds. One could pace-out various distances and see when the butterfly vanishes. Try it--and tell us at what distance your butterfly disappeared. (Final Note: When watching migrating monarchs, you may have noticed that the butterflies' movement helps us to see them. Even when butterflies appear as tiny specks in the sky, our eye can catch their movement.)

How to Respond to Today's Challenge Questions:

IMPORTANT: Answer only ONE question in each e-mail message.

1.Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question #25 (or #26).
3. In the body of EACH message, give your answer to ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on May 2, 2002

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