Not every monarch is migrating

LITTLE ROCK — What triggers monarch migration?

I saw my first monarch butterfly of the summer last weekend, supping on Mexican milkweed. Later, I looked on the undersides of the plant’s leaves and found a single, tiny, celadon-green monarch egg. A couple of colleagues also mentioned seeing monarchs on their butterfly plants. The annual migration has begun, I said to myself.

Not true. The monarchs you have seen over recent weeks are direct descendants of those butterflies that were migrating through the region last spring and stayed, instead of moving on north. That’s the word from two local butterfly experts: John Watts, entomologist with Texas Discovery Gardens and keeper of the chrysalises in the organic museum’s butterfly house, and Texas butterfly farmerDale Clark.

“The migration that comes through here is the first and second weeks of October,” said Watts, who joined the gardens a year ago. “We can never say what day exactly they will begin arriving,” but their timing is predictable.

Watts explained that the mature monarch caterpillar must receive a certain combination of meteorological and seasonal prompts that triggers its migration response. It is shorter days plus cool nights that trigger the caterpillar’s migrationgene, which, in turn, causes the caterpillar-turned-butterfly to set sail for Mexico, some via Arkansas.

“We can actually have another generation mature here,” Watts said, “and it will take a month to go through that generation’s stages.”

What that means to butterfly-loving gardeners: Be sure you have plenty of blooms. Clark said violetblue Gregg’s mistflower (Conoclinium greggii) is a top choice. It is perennial in the mid-South, blooms profusely in late summer through autumn and will take some shade. He also recommended goldenrod, sunflower, lantana and asters, among others.

The milkweed family is doubly useful for attracting and supporting monarchs, since all but one species serve as nectar and host plants. Asclepias tuberosa (orange-flowered butterfly weed) does not produce the ingredient that makes monarchs poisonous “to birds, lizards and whatever else might eat them,” Watts said.

The foul-tasting component does not protect feeding caterpillars, however, from predators. I asked Watts why a wasp was hovering over my Mexican milkweed.

To my astonishment, Watts explained paper wasps can smell caterpillars. “It chews them up and feeds them to their babies.”