Monarch caterpillar in the field

The monarch butterfly population has been shrinking for the past decade—and nobody is sure why. Many scientists have suspected a decline in milkweed plants, the monarch’s main source of nutrients, as the cause of the iconic butterfly’s dwindling numbers 

Don’t Blame Milkweed

June 14, 2016

Monarch caterpillar in the field

The monarch butterfly population has been shrinking for the past decade—and nobody is sure why. Many scientists have suspected a decline in milkweed plants, the monarch’s main source of nutrients, as the cause of the iconic butterfly’s dwindling numbers.

That might not be the case, says Cornell professor of ecology and evolutionary biology Anurag Agrawal.

In April, the Cornell Chronicle covered Agrawal’s study of monarch migration patterns over the past two decades. Agrawal and his team found that monarch numbers were not dropping in the summer breeding season, which is when they depend on milkweed. Instead, the problem seems to start when the butterflies set out on their epic migration in the fall.

In May, Agrawal followed up on his findings in an interview by Public International Radio. He suggests that there may be several factors contributing to the decreasing monarch population:

It's been very difficult to pinpoint the impact of... forest degradation on the monarchs, but it's quite clear that it is substantial... I think it's the flower resources available, the lack of uninterrupted and clean landscapes, and the [degraded] overwintering forests that may all be contributing to their decline.

Agrawal’s research was funded by a 2013 Academic Venture fund award.

Listen to the interview on Public International Radio.