(This piece was originally published in the September issue of Urban Times)
That monarch butterfly winging through your neighborhood has a whole story to tell. It’s a story of habitat loss and endangerment, but also wonder. Weighing less than a gram, this iconic species will take an incredible journey this fall.
Each autumn, monarchs migrate from summer breeding grounds to their winter grounds. The monarchs we see locally are on their way to central Mexico—a distance of up to 3,000 miles!
Summer generations of this butterfly only live two to six weeks as adults, staying local as they flit from bloom to bloom. But the generation that migrates has a much longer lifespan. They can live for up to nine months.
According to Monarch Joint Venture, a nonprofit partnership dedicated to monarch conservation, the migratory generation responds to external cues to start their southward flight. As days shorten, temperatures decline, and milkweed and nectar sources age, it triggers a shift. The monarchs that emerge by mid-August generally stop reproducing and begin to migrate—toward overwintering grounds they have never been to before.
As they fly south toward Mexico, they will stop at sites where nectar is abundant and shelter is available. In central Mexico, the entire population of eastern monarchs will land in a very small area in the mountains. There they amass in oyamel fir trees, where cool temperatures, water, and shelter enable them to survive winter.
This same generation is the one to start back north in March. They venture into Texas and southern states, laying eggs and nectaring as they migrate and breed. Their offspring (first generation) continue the journey northward, recolonizing breeding grounds as they travel through the central latitudes in April and May.
The second and third generations populate the breeding grounds throughout the summer, and the fourth or fifth generation is the one to fly south to central Mexico.
It’s not well understood how the monarchs navigate to an unknown site to overwinter, but it’s believed they primarily use an internal “sun compass.” There’s also data suggesting they have a magnetic compass that helps orient them south towards their overwintering grounds during fall migration.
Population declines stem from habitat loss and pesticide use, as well as climate change, which may force changes in their migratory patterns.
So when you see monarch butterflies flitting through parks, nature preserves and gardens this fall, know that they are on a mysterious (and perilous) long-distance marathon. And if you garden, plan now to increase your support of this and many other species by planting native plants!