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Predicting When the First Spring Generation Will Emerge

It's early May, and the monarchs from Mexico have traveled as far north as shown on the map below. When and where will their offspring emerge and continue the northward migration? Our goal is to show when we can expect monarchs to emerge at the places where the monarchs from Mexico have now arrived.

As of May 2, 2001

1. Print out a copy of Journey North's monarch migration map. Look carefully at the legend. Notice that the different colors show the range of dates when FIRST monarchs were sighted.

Remember: There were probably many, many monarchs in each place where one monarch was sighted. And what do you think the FEMALE monarchs were doing at all of those places? (Answer: Laying eggs--LOTS and LOTS of eggs!)

2. If we assume eggs were laid where these monarchs were sighted, when would the next generation of monarchs emerge in these places?

First you need to consider how long it will take for a generation to develop. Depending on temperature, the time for development varies. But an estimated number of days the monarch spends at each stage of development is:

Development Time for a Monarch Generation
Stage

# days

Egg to Larva

3-5

Larva to Chrysalis

9-14

Chrysalis to Adult

8-13

Total number of days between generations

20-32 days

3. Let's assume that it takes 32 days for a monarch to develop from an egg into an adult. Now make a new legend for the map. Our goal is to show when we can expect monarchs to emerge at all the places where the monarchs from Mexico have now arrived.

First Monarch Sighted Next Generation Should Emerge
Before March 15  
Mar 15 - Mar 28  
Mar 29 - Apr 11  
Apr 12 - Apr 26  

When and where will the offspring emerge and continue the northward migration? (Click here to see new map and legend.)


(IMPORTANT NOTE: In reality of course, monarchs are now at different stages of development all across their range. This is due to the differences in arrival dates, the different temperatures at each place, and other factors that affect development time. This question is only intended to help estimate the timing of monarch generations.)

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