Vox:

The monarch butterflies are disappearing. Over the past 20 years, fewer and fewer butterflies have been making the long journey down to Mexico to survive the winter.

Scientists have proposed a few possible reasons for the decline, from habitat loss in Mexico to bouts of unusually severe weather. But a new paper this month in the Journal of Animal Ecology argues that the biggest culprit here is likely the decline of milkweed plants in the United States — the main food for monarch caterpillars before they turn into butterflies.

The story of how these beautiful delicate creatures make their way from as far as Canada to Mexico is amazing. It would be a tragedy to see their decline.