Millions of monarchs will spend this winter in Mexico. A few years ago, butterfly enthusiast Eileen McDonnell went to see the colorful insects.

" If you tore a dollar bill in half, one half of that dollar bill would probably equal the weight of the monarch. And if you could imagine trees bending underneath the weight of monarchs."

But freezing weather last winter killed off many of the butterflies, leaving some observers worried about the long-term impact. McDonnel says she's seen plenty of butterflies stop by her flower garden this year. But this summer hasn't exactly been the best time to spot butterflies.

"With the drought, we've had fewer insects, I think just generally speaking, because many of the flowers died."

McDonnel says those flowers provide food for butterflies... which in turn are food for larger animals. When weather — or urban development — cuts back on bug food and habitat, it can set off a chain reaction affecting a whole ecosystem.

More information's available on the web at GreenWorks.tv. I'm Brad Linder.