Monarch Butterfly
Jim Gilbert

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Monarch Butterfly Update: May 26, 1998

Today's Report Includes:

Latest Migration News and Data
Monarchs appear to have flooded into the north over the past week, with butterflies now as far as 46N and 47N. You'll find 41 new sightings today for your migration map.

Latest Migration Map
As of May 26, 1998
(Compare to Spring, 1997)

Of today's 41 sightings, 12 were reported on a single day--May 19th. Do you think this is significant?

  • What percentage of this week's sightings occurred on May 19?
  • How many monarchs were reported per day for other dates last week? What percent per day?
  • Note the places where these monarchs appeared, then take a look at the weather conditions on and before May 19th. Can you identify a weather system that may have led to the large number of sightings that day?

Link to Weather Maps for:

May 16 and May 17 and May 18
(All maps show weather conditions at 6-7 pm)

  • What other factors should be considered? (Teachers should challenge students to list as many as they can. What about the behavior or location of the Journey North observers? Was it a weekend? Did these occur in heavily populated areas, suggesting there were simply more people watching? etc.)

Predators and Parasites on the Prowl

Stink Bug
Photo by FAIRS

Sucking the life from their victims, devouring the eggs, eating the young--you don't have to go to Africa to see it. You can explore the predator/prey interactions that monarchs face in your own backyard and you'll be amazed at what you see.

I certainly was! Right before my eyes, my monarch caterpillar suddenly split open--and out crawled 3 maggots. It was like science fiction....The white larvae, I learned later, were tachinid flies. The adult tachinid fly lays its eggs on monarch larvae--and the young flies develop inside. Just before my monarch became a chrysalis, the fly larvae emerged. (I was curious, so I kept them. They developed into adult flies within a few days....Not as nice as monarchs, maybe, but fascinating.)

Keep in mind: A single female monarch butterfly can lay several hundred eggs. If they all survived, the world would be overcome with monarchs. Predators play a significant role in keeping the balance--but nobody really knows their impact on overall monarch abundance. This summer, you can help scientists study these questions. See:

Predator Watch

Michele Prisby, U. of MN, demonstrates the exclosure she invented to contain monarch larvae.

You can also simply find a few milkweed plants and standby. Spiders, ants, predacious wasps, milkweed bugs, stinkbugs, mites and many others are known to prey on, or parasitize, monarch eggs and larvae. Sketch the different creatures you find on milkweed and try to identify them. Build an exclosure around several milkweed plants. Do more monarch larvae seem to survive when protected inside the exclosure? Try to quantify your observations.

Protection in the Bag!
A Monarch Watch contributor suggested protecting monarch eggs and larva by using mesh paint filter bags to cover the milkweed plants. The bags are about 5 gallon size, available at paint stores, and inexpensive.

Before covering the milkweed, carefully look the plant over and remove any existing potential predators. Then, gently pull the bag over the plant, and secure the bag at the base of the stem with a twist tie. But be careful--check the bag periodically, because one larva may eat the whole plant before you know it and need to be moved to another plant!

Monarch larvae develop through 5 stages, called "instars". Learn how to recognize each stage:

Photos & Information About Some Monarch Larvae Parasites & Predators

Reminder: When School's Out the Monarch Migration Will Continue
Although this is our our last scheduled update, we're not going away. We will continue to collect your monarch sightings daily. Every Tuesday, watch for a new migration map and data update until the monarchs have completed their journey north.

Journey North
Year End Evaluation
Please share your thoughts

The Next Monarch Butterfly Migration Update Will be Posted on June 2, 1998.

Copyright 1998 Journey North. All Rights Reserved.