Spring Migration North
Click here for Fall Migration South
Every Spring, monarchs leave their overwintering sites in California, Mexico and the
Southern United States around
mid-February, begin mating and looking for milkweed to lay their eggs. East of the Rockies their movement
is to the Northeast to Northwest until mid-June, then they tend to stay in the
local area. During the time of movement, there are several generations of butterflies,
usually three to four. (There can be as few as two generations
and as many as five each year.)
In most years
in the East, by the time monarchs reach a latitude of 39 to 40 degrees (dotted yellow line)
all the the monarchs who overwintered have died and the new generations move forward.
How this works in the West is less well known.