This is horrific. We’ve lost over 80% of the butterflies.
The waning of our monarchs has lead to the inevitable speculations as to the cause. Which is fair enough. But I’d like to point out the ideas are just speculation.
No one really knows why Monarchs are declining, or why 2012-13 is such a bad year.
Lacking the proper experiments to determine how various factors affect the butterflies, and lacking solid data about their milkweed food sources, assigning causes to the phenomenon simply isn’t possible. The monarchs are disappearing. That’s all we can say with certainty.
Candidate causes abound, though.
- The severe heat and drought of 2012 across much of the monarch’s summer range may have reduced the monarch’s host plants and stressed the remaining animals.
- The extensive use of agricultural herbicides in conjunction with herbicide-resistant crops could be eliminating the monarch’s food supply, perhaps causing the gradual decline over the past 10 years.
- The destruction of milkweed habitat for corn ethanol production, also a gradual new phenomenon in the past 10 years, could reduce the monarch’s food.