40 
FINDING NATURE’S TREASURES 
becomes cold in the fall. It is their babies which live as 
pupas during the winter, and then hatch into butterflies 
when it becomes warm in the spring. Those butterflies 
do not travel south for the winter. But the Monarch 
butterflies gather on the trees in great numbers when 
they are getting ready to go south. There are sometimes 
enough butterflies hanging together to fill a large basket. 
They all leave before the winter storms begin, and do 
not return until the milkweeds begin to grow in the 
spring.” 
“What are milkweeds?” inquired Fred. 
“They are plants with large, thick leaves. When the 
leaves are broken, the sap comes out like drops of milk. 
But the sap does not taste like milk; it is bitter and sticky. 
The babies of this butterfly will eat nothing but the milk¬ 
weed which grows in the north. The mother butterfly 
travels hundreds of miles, so that she can lay her eggs on 
these plants. You could never guess why it is that birds 
do not try to catch and eat her, while she is traveling 
so far.” 
“I thought that birds ate all kinds of butterflies when¬ 
ever they could catch them,” said Bess. 
“They do like many kinds of butterflies, but they 
have learned that this butterfly does not taste good,” 
said Uncle Jack. “The birds not only leave it alone, but 
they will not touch any other butterfly that looks like it. 
There is a butterfly known as the Viceroy which is really 
very good for birds to eat. But the Viceroy looks so 
much like the Monarch that it fools the birds. They think 
it is the Monarch and never eat it.” 
