How
Many Monarchs in This Fortyacre Field?
Information
we had to start with:
 The
field is 40 acres.
 The
monarchs are 8 feet apart.
Information
we needed to look up:
 One acre
is 43,560 square feet
The
steps we took to solve the problem:
 We began
with some graph paper so we could draw a picture and see the situation.
 We knew
there was one butterfly every 8 feet. We decided to let the length of
each square represent one foot. We spaced the butterflies 8 squares
apart.
 Notice
that there must be 8 feet between the butterflies in all directions.
Here's our graph paper so you can see the spacing between the butterflies.
(Click
to enlarge.)
 Because
there are 8 feet between each butterfly, each butterfly is surrounded
by 64 units (square feet) of space. In other words, there is only one
butterfly for every 64 square feet.
 You can
click on the graph to count the 64 units (or "square feet")
of space surrounding each butterfly.
 We divided
the 43,560 square feet in an acre by the 64 square feet needed for each
butterfly and found there were 680 butterflies per acre.
(43,560/64 = 680)
 The
field is 40 acres, so there are 27,200
butterflies in the 40acre field!
More
About Monarchs and Alfalfa
The 40 acres of alfalfa pictured above is a magnet for hungry butterflies.
The monarchs are looking for nectar and alfalfa flowers are a good source.
When the
monarchs travel through the Midwestern states they are surrounded by
corn and soybean fields. In fact, as much as 90% of the land is now
planted with crops where there was once prairie.
Only lucky
monarchs find alfalfa in bloom. Farmers usually cut alfalfa before it
turns to flowers. This is because farmers grow alfalfa for hay to feed
their milk cows. The food value of the hay goes down when it's allowed
to flower. (The plants use energy to make the flowers.)
Imagine
you're a butterfly looking for flowers the next time you travel. What
does the landscape look like to you? Can you find flowers easily?
