APRIL 2015 • NEBRASKAland 31
from man. But the North American monarch is the only
butterfly in the world that migrates. Other butterflies and
moths emigrate, moving to find warmer weather or food, but
their young make the return flights.
Monarchs west of the Rockies, which make up 5 percent
of the world's population, follow a similar routine, but
migrate only as far south as southern California. Scientists
still aren't sure how the rest of North America's monarchs
find their way to Mexico, some traveling up to 3,000 miles,
an amazing feat for a bird, much less an insect. Yet by
November, nearly every surviving butterfly from east of the
Rocky Mountains has arrived in a small, mountainous area
west of Mexico City.
In Mexico, the wintering monarch population, which
are known to occupy only 11 to 14 sites, is estimated by
surveying the area the butterflies cover. In the winter of
2013-14, that number hit an all-time low of 1.65 acres, down
from a high of 51.8 acres in 1996-97. Researchers estimate
this 90 percent decline had left just 33 million monarchs.
Things improved slightly this year, with monarchs covering
2.8 acres.
But in the past, winter storms in the mountains have led
to catastrophic population declines. With so fewer monarchs
remaining, the effects of such losses could be much more
dire for the rest of the population.
Milkweed and Monarchs
Logging in the monarch's winter home, and the possible
loss of roost trees, was feared as the major threat to the
butterfly until recently. With the creation of reserves by
the Mexican government, that threat has been minimized.
Researchers only recently realized the loss of milkweed
throughout the insects' range is of equal concern.
The metamorphosis of a monarch begins as a pinhead-
sized egg that females lay on the underside of the leaf on
A pair of monarch butterfiles feed on butterfly milkweed nectar (A. tuberosa) in a restored prairie in Lincoln. The species only lays
its eggs on milkweed, and the decline of the native wildflower has been tied to the monarch's decline. Other milkweeds
native to Nebraska include common, swamp, prairie, whorled and showy.
