Monarch butterflies could disappear from Eastern US within 20 years

(credit: Sandy/Chuck Harris)

In colder climes, signs of spring can lift a heavy weight from a tired, frozen spirit. Trees bud, flowers bloom, and migratory species trickle in to announce the approach of summer. In the US, one of those species is a floppy orange gem: the monarch butterfly. These insects winter in amazingly dense clusters in Mexican forests before making a staggeringly long journey (one that spans multiple generations, in fact) to summer homes to the north.

But in recent years, the population of monarchs that stay east of the Rockies has dropped like a rock. Precise population numbers are difficult to come by, but estimates kept by the US Fish and Wildlife Service show about an 80 percent decline over the last decade.

Unfortunately, it appears that humans are responsible. The life cycle of the monarch is tightly linked with the milkweed plant. Females lay almost all of their eggs on these plants, and the larvae happily munch on them when they hatch. Milkweed tends to pop up in areas where the soil has been disturbed, like farm fields.

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