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Monarch Butterfly Migration Update: April 11, 2002

Today's Report Includes:

Latest Migration Map and Data

Migration Data

Milkweed Data

As this week?s migration map shows, it?s been a slow week with only a few new locations added. This lull occurs each year, as the lives of the overwintering generation wane and the next generation develops. One is left with the impression that the monarchs from Mexico are largely scattered across Texas?s 262,015 square miles, and only a small percentage have reached the other states from which they?ve been reported. This spring's small population, coupled with the late spring freeze and slow milkweed development, may explain why the migration has not spread further.

  • But what are some other possible interpretations for so few reports this week? (Think carefully about possible ways the behavior of our observer network could affect the migration map.)

First of the Spring Generation Emerges in Texas Classroom
From the tip of southern Texas, students at Weslaco East High School witnessed what?s about to occur across their state:

?Six monarch butterflies emerged on April 4 in our classroom. These may very well be some of the first monarchs of the spring generation here in Texas.The eggs were gathered on March 11 from wild A. oenotheroides growing in McAllen, Texas. We fed the larvae, guarded each chrysalis, and watched the 4 females and 2 males emerge Thursday morning.?

The first big wave of migration entered Texas at the same time these eggs were laid, so the number of monarchs on the wing is about to increase dramatically!

Challenge Question #22
?How many days did it take the McAllen, TX monarchs to develop, from egg to adult??

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

Expecting Monarchs in Arkansas
Now How Many Eggs Has She Laid?

Back to the famous female monarch in Arkansas, who arrived 16 days after the Mcallen, TX monarchs:

?Everybody is doing well here,? says Jim Edson. ?The female has laid 211 eggs as of this afternoon, April 9. Some of the caterpillars went to live in my granddaughter's kindergarten class today. They enjoyed seeing the little mother in person and on the Journey North webpage. Here are some pictures to show some of the growth. By the way, the outside eggs started hatching over the weekend (April 5-7). I have only been able to find two of the larva. I think the wasps are getting them.?

Photos 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

Your Predictions Please!
Challenge Questions #19, #20 and #21

Challenge Question #19
"On what date do you think Jim Edson's first monarch of the next generation will emerge in Arkansas?"

Challenge Question #20
"How many eggs do you predict the female from Mexico will lay in captivity?"

Challenge Question #21
"On what date do you think the female from Mexico (of the over-wintering generation) will die?"

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

What is an Instar?

?We don't understand the life cycle chart. What is an instar molt?,? asked one reader.

The life cycle of a monarch includes four stages: egg, caterpillar (larva), chrysalis, adult.

Basically, during the time a caterpillar grows, it "molts" 5 times before it becomes a chrysalis. Its skeleton is on the outside of its body, like clothes. So as it grows it can no longer fit in its skin. Instars are stages of caterpillar growth. Each time it molts the caterpillar progresses to the next instar (1st instar, 2nd instar, 3rd instar, etc.)

Can you see the shedded skin, behind the caterpillar?
Photo: Jim Edson

But as Dr. Lincoln Brower explains, the analogy of growing out of clothes doesn?t fit exactly. ?The caterpillar doesn?t just shed that skin, it digests and reabsorbs most of it. Before the skin starts shedding it does get tight. But it doesn?t just slip off. What happens is that the cells beneath the skin start releasing enormous amounts of enzymes and actually absorb most of the skin. Before it?s shed it becomes a thin sheen over the body. So what is shed is just a thin outer part of the cuticle. You?ve seen how it looks when shedded, right? (See picture on right.) Sort of like a snake?s skin. So a snake skin analogy is really much better.?

Some definitions:

  • Cuticle--the proper name for the skin or exoskeleton of the caterpillar.
  • Epicuticle--a waxy layer on the outside of the cuticle that protects the caterpillar from water loss.
  • Chitin(pronounced ?kite in?)--found in the cuticle, this is the material that makes the exoskeleton of an insect strong and lightweight, and protects its soft insides. Chitin can be thin and pliable, as it is in the monarch caterpillar stage. Or, if thick, chitin protects the insect with a hard, rigid exoskeleton.

Monarch Lab: Field Guide to Monarch Larvae
You?ll find excellent field marks to help you distinguish between the different caterpillar instars on Dr. Karen Oberhauser's Monarch Lab Website.

Female Egg-Laying Strategy?
Discussion of Challenge Question #18

Unlike people, who take care of their offspring for at least 18 years, a female butterfly's job as a parent is finished as soon as she lays her eggs. We asked "Why do you think female monarchs typically avoid laying more than one egg on a milkweed plant? List all the benefits you can think of."

Students put their heads together and came up with these reasons:
  • Enough food for each caterpillar when they are hatched from the eggs.
  • Less of a chance for all of the eggs to get eaten by predators.
  • They are more camouflaged from predators if there is only one egg on a leaf.
  • A predator might not see it if there is only one egg on each leaf.
  • If that plant dies, not all of the eggs will die.
  • Anything that starts eating the milkweed would only destroy one egg.
  • If there are too many on it, the leaf could break and they could die.

Thanks to these people for sharing their thoughts!

  • Nick and Lane, Grade One at Ferrisburgh Central School in Ferrisburgh, VT
  • Ms. Prete?s third grade at GLH Johnson Magnet School in Danville, VA
  • Mrs. Bowles Science class at GLH Johnson Magnet School in Danville, VA.
  • Mr. Deneen's, Mrs. Flaherty's, Ms. Macko's and Ms. DiBara's second grade classes at Charlotte Dunning School in Framingham, MA
  • Darrell Atteberry Home School and Pat Thomas of Duluth, MN

A Day in the Life of a Butterfly Egg
Mother monarchs abandon their eggs the instant they're laid. If you were a butterfly egg, your mother couldn't afford the time to raise you. You'd be just one of the several hundred siblings she'd try to produce in her short life. Read what she?d so to increase your chances of survival. Then go on an insect egg hunt!

How High Were the Monarchs Flying?
Discussion of Challenge Question #17

We asked, "How high in the sky were those monarchs traveling in Dallas??

Ms. Lara's 3rd and Mr. Larson's 4th grade classes DeMiguel Elementary School Flagstaff, AZ estimated 102 meters. They measured their classrooms to get the height of one story, then multiplied by 32 stories.

Mrs. Bailey's Fifth Grade class at Ellen Smith Elementary in Conway, Arkansas estimated 97 meters high. ?Each floor is about 3 meters high. Our class wanted to find out if we could identify the building in Dallas. We came up with some possibilities: Elm Place, Renaissance, or Bryan Tower,? they said.

?The kids are very close,? responded Zoe Broxon from the 32nd floor in Dallas.?The building is One Main Place which is across the street from Rennaisance and Elm Place. The building is 32 stories high and each story is approximately 10 feet.? (Multiplying that out, we get 320 feet tall which or 97.5 meters.)

So, one fact we know about spring monarch migration is that, at least over a city, monarchs may travel quite high. They don?t always fly low, near the ground, nectar and milkweed.

Challenge Question #23
?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??

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

Permanent Database for Your Own Monarch Records
See the sightings you've submitted over the years! Use Journey North?s permanent online database to store your historic records.

Phenology is the study of the seasonal timing of life cycle events. All of the observations you report will be stored here.

Answers from the Monarch Expert
Special thanks to Dr. Karen Oberhauser for sharing her time and expertise to answer students? questions again this year!

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 #22 (or #23)
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 April 18, 2002

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