Monarch butterflies are disappearing. Scientists agree that in the last 20 years, populations of the black and orange insect have been in precipitous decline. But there's much less certainty on what’s causing them to vanish.
As each new scientific paper on monarch decline is published, the image becomes slightly less opaque. So far, potential culprits include disease, climate change, drought, deforestation, and sparse nectar plants. Blame has been cast on everyone from loggers to farmers to suburban developers.
In the battle to save the migratory monarch, advocates have zeroed in on a simple, leafy weed.