Monarch
Generations
Which Generation Goes to Mexico in the Fall?
Spring
is the beginning of the monarch's breeding season. In March, the monarchs
migrate north from Mexico. They breed in the southern United States
in March and April, and then they die. At that time they are 7-8 months
old. They were born as early as August, survived fall migration, a long
winter, and spring migration to the southern U.S. In contrast, during
the summer breeding season, monarchs live for only 2-5 weeks! Several
generations live and die each summer, and it's the final generation
that migrates to Mexico in the fall. (See Monarch Annual Cycle slideshow.)
Activity
1) Using the worksheet below, you can figure out which generation
migrates to Mexico. Here is the question: Of the monarchs that spent last
winter in Mexico, do you think this fall's migratory generation
will be:
- their
children?
- their
grandchildren?
- their
great-grandchildren?
- their great-great-grandchildren?
- their
great-great-great-grandchildren?
- their great-great-great-great-grandchildren?
- ....you
have the idea, now see if you can calculate the answer!
2) First
you need to know how long it takes for one monarch generation to develop:
Development
Time for a Monarch Generation
Stage |
#
days |
Egg
to Larva |
3-5
|
Larva
to Chrysalis |
9-14
|
Chrysalis
to Adult |
8-13
|
Days
before adult female is old enough to lay eggs |
5
|
Total
number of days between generations |
25-37 days |
Average
number of days |
_____ days |
3) Use the
chart below to calculate the development date for each generation. Assume
the first eggs are laid on March 15th, by the monarchs that overwintered
in Mexico.
4) Fill in
the blanks for each new generation by adding the average number of
days for a generation to develop.
5) Monarchs stop laying eggs in the north in late summer, when the days
begin to get shorter, the temperatures drop and milkweed stops growing.
For this example, use August 15th as the date the eggs of the last generation
are laid. That is, when you get to August 15th on the chart below--stop!
This is the generation that will migrate to Mexico!
Generation
Number |
Generation
Name |
1st
Date this generation ready to lay eggs |
0
|
Over-wintering
generation (monarchs from Mexico). |
March
15 |
1st
|
Children
of monarchs from Mexico |
__________
|
2nd
|
Grandchildren |
__________
|
3rd
|
Great-grandchildren |
__________
|
4th
|
Great-great-grandchildren |
__________
|
5th
|
Great-great-great
grandchildren |
__________
|
6th
|
Great-great-great-grandchildren |
__________
|
Important
Note:
These are estimates! In reality of course, the time for a generation to
develop varies, based on temperature and other factors. This question
is only intended to help estimate the timing of monarch generations.
Extension:
1) There are many assumptions, averages and estimates in this activity.
Each one affects the answer you get. How many can you find? If you change
some of the assumptions, averages and estimates, how does
it affect the answer?
2) If you live in the monarch's summer breeding range, you can use this
chart to keep track of the generations that develop this summer where
you live.
- Watch
for eggs on your milkweed plants.
- Bring
one or two inside, where they're safe from predators.
- Count
how many days it takes for them to develop. (Be sure to keep temperatures
the same as outdoor normal temperatures, so the development time will
be the same. A screened porch is ideal!)
3) A female
monarch can lay eggs throughout her 2-5 week lifetime, and a single female
lays hundreds and hundreds of eggs. What does this mean about monarch
generations? (Answer: There is a great deal of overlap between generations.)
|