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Spring Migration North
Click here for Fall Migration South
Every Spring, monarchs begin mating around mid-February, then leave their overwintering sites in California, Mexico and the
Southern United States looking for milkweed to lay their eggs. Breeding monarchs only live two to five weeks, or an
average of about a month. When monarchs in one generation reach the end of their lives, their offspring (eggs, larvae and pupae)
continue to mature. When new monarchs eclose, the cycle repeats, expanding their range. East of the Rockies their movement
is generally to the north and northeast until mid-June, then they tend to stay in the
local area and continue breeding. During the time of the spring migration, there are several generations of butterflies,
usually three to four. (There can be as few as two generations and as many as five or more 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. However, citizen scientists have documented
spring migration movement in several locations in the southwest.
- Along the Colorado River on the Arizona-California border
- In Tacna and Dateland in southern Arizona
- Along the San Pedro River in Arizona
- Along the Rio Grande River in San Antonio, New Mexico
- Las Vegas wash, east of Las Vegas, Nevada
- The low deserts of southern Arizona and southeastern California
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