Save the Monarchs

Forrest M. Mims III

Are milkweed plants growing in your yard or on your land? If you avoid mowing them this spring you might help boost the population of monarch butterflies.

How? Milkweed leaves form the diet of the colorful caterpillars that eventually become monarch butterflies.

After spending the winter in their famous groves in the mountains near Mexico City, monarch butterflies have been flying through Texas during their annual spring migration. Some of their descendants will eventually make it to New England and even Canada, and that process has already begun.

A week before the Easter cold wave hit Texas, a monarch was flying erratically around the field I call Geronimo Creek Observatory. She would occasionally dip down to the ground for a few seconds and then resume her back and forth flight path.

I knew the butterfly was a female, because I’ve observed this behavior many times before. So I walked over to two of the places where she had briefly landed and looked for milkweed plants.

As expected, there was a milkweed plant at both places. It didn’t take long to find several tiny monarch eggs smaller than this “o" attached to leaves. The cream-colored eggs resembled footballs with fluted sides.

Figure 1. : This monarch butterfly caterpillar emerged from an egg (upper left) about two weeks before this photo was made. Fire ants (circle at bottom) do not bother monarch caterpillars. Photograph by Forrest M. Mims III.

Five days after Easter, I checked on the milkweed eggs. All three were gone, and nearby were tiny monarch caterpillars with their characteristic yellow, black and white bands. Fire ants were nearby, so I wondered if the caterpillars would survive.

Two days later, the caterpillars were still chomping away on the milkweed leaves, and they were noticeably bigger. As I watched, one caterpillar climbed onto a blade of grass. Soon it was several inches away from dinner, for monarch caterpillars eat only milkweed. So I bent the grass over a milkweed leaf and the caterpillar returned home.

That evening, one caterpillar was missing. I found it more than a foot away from its milkweed and returned it to where it belonged.

Each time I have checked on these caterpillars, fire ants have been prowling nearby, often on the same leaves the caterpillars are eating. Twice a fire ant walked directly up to a caterpillar and then quickly left.

It’s well known that most birds don’t like monarchs because of the milkweed diet they enjoyed as caterpillars. So perhaps the monarch caterpillars emit something that repels fire ants.

It’s been three weeks since I found the first monarch eggs of 2007 on our place. Yet even as this column was being written another monarch paid a visit and left behind more eggs than the first. So it looks as if the two dozen or so milkweed plants in our field might produce a nice crop of monarchs over the next several weeks.

You can learn much about this remarkable creature and find out about monarch tagging projects at Monarch Watch, a program of the Kansas Biological Survey at the University of Kansas.

"World of Science" columns are selected and sometimes revised from columns published in the San Antonio Express-News or the Seguin Gazette-Enterprise. The columns are intended for a general audience. Forrest M. Mims III and his science are featured online at www.forrestmims.org and www.sunandsky.org .